[EPIC] 0.7.0 MiniMaxConfig name collision resolution (#190)

## Goal

Ship a coordinated **0.7.0 minor release** that resolves the
`MiniMaxConfig` name collision across `voxora-config` and
`voxora-minimax` so consumers can wire both into a single file
without the silent-shadowing surprise described in
[#190](https://github.com/airvzxf/voxora/issues/190).

## Members

### Breaking change (the only member)

- **#190** — rename `voxora_minimax::MiniMaxConfig` →
`MiniMaxEngineConfig` (or `MiniMaxSettings`). The user-facing
`voxora_config::MiniMaxConfig` stays unchanged (the rename
is purely internal to the engine crate). Add a deprecation
alias `pub type MiniMaxConfig = MiniMaxEngineConfig;` in 0.6.x
so consumers that hit the collision via the indirect
re-export path (`voxora_bridge::MiniMaxConfig`) get a clear
migration message.

## Acceptance

This EPIC closes when:

- `voxora-minimax::MiniMaxConfig` no longer exists by that
name; only `MiniMaxEngineConfig` (or equivalent) is exported.
- The user-facing `voxora-config::MiniMaxConfig` is unchanged.
- The 0.6.x deprecation alias is in place, producing a clear
`#[deprecated]` lint for any consumer that still imports the
engine's old name.
- All workspace crates that participate ship at 0.7.0 per
`AGENTS.md` § "Version coordination" (this is a breaking
change so the minor bump is mandatory for everyone that
re-exports the renamed type).
- `cargo fmt --all --check`,
`cargo clippy --workspace --all-targets -- -D warnings`,
`cargo test --workspace --all-targets`,
`RUSTDOCFLAGS="-D warnings" cargo doc --no-deps --workspace`
are all green.

## Strategy

The 0.6.x series already shipped the typed `AsrError::LockUnavailable`
variant and the `max_bytes` enforcement (PRs #229, #230). The
0.7.0 EPIC is purely the rename + the deprecation alias. Land as
one PR + one minor release. Independent of EPIC #206 (which
closed in 0.6.2).

## Cross-references

- The local source's `max_id_length` cap (EPIC #148, 0.5.3) is
the prior art for "additive API surface with field-level
validation".
- The deprecation alias pattern is the same as
`voxora_bridge::ModelSource` (re-export of `voxora_traits::ModelSource`)
— a single type re-exported through the umbrella crate so the
workspace can stay compiled while consumers migrate.

## Out of scope

- Any change to the user-facing `voxora_config::MiniMaxConfig`
struct (env-var cascade, CLI flag plumbing, etc.) — those
belong on their own EPIC if a future release needs them.
- The `voxora-http` factor-out from #162 and the
`voxora-openai-asr` engine from #163 — already `pending-human`
(operator decision on hosted-API roadmap).

## Labels

epic, breaking-change, refactor