refactor(llm)!: delete legacy Provider trait + 5 impls + BreakeredProvider + ProviderRegistry + wire.rs + wire_format.rs (BREAKING v0.18.0)

## Goal

Delete the legacy `Provider` trait + the 5 concrete `Provider` impls + the `ProviderRegistry` + the `BreakeredProvider` wrapper. After this issue lands, `src/llm/provider.rs` is gone; `src/llm/minimax.rs`, `src/llm/deepseek.rs`, `src/llm/anthropic_compat.rs`, `src/llm/openai_compat.rs`, `src/llm/openai_compatible.rs`, `src/llm/mock.rs` are gone. Only `src/llm/client/*` (introduced across #1-#14) remains.

## Why now

After #5-#14 finish migrating every `Provider::` consumer in `src/` to `LlmClient`, the legacy types have zero production consumers. The only remaining references are the test stubs (`ScriptedProvider`, etc.) and the `ProviderRegistry::from_config` chain — both migrated by #11. Deleting the legacy files is the **only** breaking change in the EPIC, and it's the change that justifies the v0.18.0 minor bump per #900 D3.

## Scope

**In scope (delete):**

- `src/llm/provider.rs` (4,449 LOC) — `Provider` trait, `ProviderRegistry`, `BreakeredProvider`, `ProviderPoolEntry`, `ProviderPool`, `registry_from_config` family.
- `src/llm/minimax.rs` (1,423 LOC).
- `src/llm/deepseek.rs` (340 LOC).
- `src/llm/anthropic_compat.rs` (1,119 LOC).
- `src/llm/openai_compat.rs` (1,951 LOC).
- `src/llm/openai_compatible.rs` (1,520 LOC).
- `src/llm/mock.rs` (589 LOC).
- `src/llm/wire.rs` (781 LOC) — `Request`/`Response`/`CallRecord`/`Usage` types, replaced by `LlmRequest`/`LlmResponse`.
- `src/llm/wire_format.rs` (894 LOC) — `WireFormat` trait + `WireFormatId` enum + `wire_format_from_url` (replaced by `client::dispatcher::pick_sdk` from #4).
- `src/llm/probe_table.rs::MaxTokensTable` (move into `src/llm/client/` or `src/llm/probe_max_tokens.rs`).
- `src/llm/temperature_probe.rs::TemperatureTable` (move into `src/llm/client/` or `src/llm/probe_temperature.rs`).
- `src/llm/param_rejections.rs::ParamRejectionsTable` is **kept** (used by the new `LlmClient::send` cascade).
- The `BreakeredClient` adapter (introduced in #5) becomes the primary circuit-breaker wrapper — rename to just `BreakeredClient` (already that name) and stop being an adapter.
- `ScriptedProvider` test stubs (kept under `#[cfg(test)]` annotations only if other test files still reference them — otherwise deleted).

**Out of scope (kept):**

- `src/llm/param_rejections.rs` — the cascade detection logic stays.
- `src/llm/capabilities.rs` — the capability matrix is reused by `LlmCapabilities`.
- `src/llm/http.rs` — the wire-body hash function stays (used by `LlmClient::body_sha256`).
- `src/llm/cache/`, `src/llm/embed/`, `src/llm/prompts/`, etc. — unrelated subsystems.
- `src/llm/probe_top_p.rs` and `src/llm/probe_top_k.rs` (introduced in #12) — these are new files; the deletion here is only of legacy code.

## Approach

### 1. Pre-flight: confirm zero `Provider::` consumers

```bash
rg 'use crate::llm::Provider|use moagan::llm::Provider|use crate::llm::provider::Provider' src/ tests/
```

Expected output: no matches. If any match remains, it's a missed migration — fix before this issue lands.

```bash
rg 'use crate::llm::provider::|use crate::llm::minimax|use crate::llm::deepseek|use crate::llm::anthropic_compat|use crate::llm::openai_compat|use crate::llm::openai_compatible|use crate::llm::mock' src/ tests/
```

Expected output: no matches.

### 2. `src/llm/mod.rs` rewrite

The new `src/llm/mod.rs` exports only the new modules:

```rust
//! LLM module: client trait + SDK impls, role enum, wire types, mock + minimax
//! implementations, cache, rate limiter, circuit breaker, and the
//! versioned prompt registry.

pub mod cache;
pub mod capabilities;
pub mod circuit_breaker;
pub mod client; // NEW (issues #1-#14)
pub mod control_tokens;
pub mod cost;
pub mod embed;
pub mod governor;
pub mod http;
pub mod json_extractor;
pub mod json_strategy;
pub mod max_tokens;
pub mod modal_gate;
pub mod models_dev;
pub mod param_rejections;
pub mod probe_max_tokens; // moved from probe_table.rs
pub mod probe_temperature; // moved from temperature_probe.rs
pub mod probe_top_p; // NEW (issue #12)
pub mod probe_top_k; // NEW (issue #12)
pub mod prompt_cache;
pub mod prompts;
pub mod rate_limiter;
pub mod response_format_opt_out;
pub mod retry_budget;
pub mod role;
pub mod size_limits;
pub mod sse_parser;

pub use client::{LlmClient, LlmRequest, LlmResponse, LlmCapabilities, LlmError, MockClient, AnthropicClient, OpenAIClient, OpenAIVariant};
pub use models_dev::{...}; // unchanged
pub use role::Role;
pub use probe_max_tokens::MaxTokensTable;
pub use probe_temperature::TemperatureTable;
pub use probe_top_p::TopPTable;
pub use probe_top_k::TopKTable;
```

The 7 legacy modules (`provider`, `minimax`, `deepseek`, `anthropic_compat`, `openai_compat`, `openai_compatible`, `mock`, `wire`, `wire_format`) are removed from the export list. Their files are deleted from disk.

### 3. `BreakeredClient` becomes the primary wrapper

`BreakeredClient` (introduced in #5 as an adapter over `BreakeredProvider`) becomes the only wrapper. It owns the breaker, rate limiter, max_tokens_table — same fields as today's `BreakeredProvider`, but wraps `Arc` instead of `Arc`.

The wrapper is constructed in `client::dispatcher::build_client` (from #4):

```rust
pub fn build_client(...) -> Result> {
let inner = match pick_sdk(endpoint)? {
SdkKind::Anthropic => Arc::new(AnthropicClient::new(cfg, api_key)?),
SdkKind::OpenAIChat => Arc::new(OpenAIClient::new_chat(cfg, api_key)?),
SdkKind::OpenAIResponses => Arc::new(OpenAIClient::new_responses(cfg, api_key)?),
SdkKind::Mock => Arc::new(MockClient::empty()),
};
let breaker = CircuitBreaker::new(breaker_cfg);
let wrapped = BreakeredClient::new(inner, breaker);
Ok(Arc::new(wrapped))
}
```

### 4. `LlmClientRegistry` becomes the primary registry

The new `LlmClientRegistry` (introduced in #11) becomes the only registry. The legacy `ProviderRegistry` is deleted.

### 5. ScriptedProvider stubs deletion

After the migration wave + tests migration (#11), `ScriptedProvider` should have zero remaining consumers. Verify:

```bash
rg 'ScriptedProvider' src/ tests/
```

Expected: no matches. If matches remain, they're test stubs that need migration or deletion.

## Acceptance criteria

- [ ] `cargo build --release --all-features` succeeds with **zero warnings** (the legacy code is gone, no dead references).
- [ ] `make fmt-check guard-deps lint build test-ci` green.
- [ ] `src/llm/provider.rs` deleted from disk.
- [ ] `src/llm/minimax.rs` deleted from disk.
- [ ] `src/llm/deepseek.rs` deleted from disk.
- [ ] `src/llm/anthropic_compat.rs` deleted from disk.
- [ ] `src/llm/openai_compat.rs` deleted from disk.
- [ ] `src/llm/openai_compatible.rs` deleted from disk.
- [ ] `src/llm/mock.rs` deleted from disk.
- [ ] `src/llm/wire.rs` deleted from disk.
- [ ] `src/llm/wire_format.rs` deleted from disk.
- [ ] `rg 'use crate::llm::Provider|use crate::llm::provider' src/ tests/` returns no matches.
- [ ] `rg 'use crate::llm::minimax|use crate::llm::deepseek|use crate::llm::anthropic_compat|use crate::llm::openai_compat|use crate::llm::openai_compatible|use crate::llm::mock' src/ tests/` returns no matches.
- [ ] `src/llm/client/` is the only LLM-traits module.
- [ ] `BreakeredClient` is the only circuit-breaker wrapper.
- [ ] `LlmClientRegistry` is the only registry.
- [ ] Smoke: `moagan run --mode fast --provider mock:mock-model` produces `final/portfolio.md` and `rankings/ranking.json`.
- [ ] Smoke: `moagan run --mode deep --provider mock:mock-model` produces all the deep-mode artefacts.
- [ ] Smoke: `moagan probe temperature --provider mock:mock-model` produces `/temperatures_auto.toml`.
- [ ] Smoke: `moagan probe max_tokens --provider mock:mock-model` produces `/max_tokens_auto.toml`.
- [ ] CHANGELOG entry: **BREAKING**: removed `Provider` trait and 5 concrete impls (`MinimaxProvider`, `DeepSeekProvider`, `AnthropicCompatProvider`, `OpenAICompatibleProvider`, `OpenAICompatProvider`). Operators with custom `Provider` impls (downstream of `crate::llm::Provider`) need to migrate to `LlmClient`. The 3 SDK impls (`AnthropicClient`, `OpenAIClient`, `MockClient`) cover all current use cases.

## Merge order

```
#1-#14 (foundation + migration + features + cleanup)
↓
#15 (this issue — legacy deletion)
↓
#16 (docs + close EPIC)
```

**Breaking change** — this issue is the only one in the EPIC that breaks the public API. Per #900 D3, no soft-landing: operators with custom `Provider` impls must migrate in lockstep with this release.

## Validation

- `make fmt-check guard-deps lint build test-ci` green after the PR lands.
- 11 files deleted from disk.
- 4 smoke runs (fast mode, deep mode, probe temperature, probe max_tokens) all succeed.
- CHANGELOG entry marked **BREAKING**.

## Version target

**v0.18.0.** This is the breaking-change release.

## References

- [EPIC #847](https://github.com/airvzxf/moagan/issues/847) — the umbrella.
- [#900 D3, D8](https://github.com/airvzxf/moagan/issues/900) — D3 (no soft-landing, breaking changes allowed), D8 (no compat layer, `BreakeredProvider` deleted).
- [ADR-0010](../blob/main/docs/adr/0010-llm-client-trait-impl-plan.md) — the deferred plan this issue finalises.