Type incompatibility when @anthropic-ai/sdk >= 0.82.0 is installed alongside claude-agent-sdk

## Description

When `@anthropic-ai/sdk@0.82.0` is hoisted alongside `@anthropic-ai/claude-agent-sdk@0.2.90`, TypeScript produces type errors because the SDK added `ToolReferenceBlockParam` to the `ContentBlockParam` union in 0.82.0, but `claude-agent-sdk`'s bundled types (built against `^0.74.0`) don't include it. This causes a type mismatch wherever `ContentBlockParam[]` is passed into agent SDK functions.

## Reproduction

`package.json`:
```json
{
"dependencies": {
"@anthropic-ai/claude-agent-sdk": "^0.2.90",
"@anthropic-ai/sdk": "^0.82.0"
},
"overrides": {
"@anthropic-ai/sdk": "^0.82.0"
}
}
```

Any code that passes `ContentBlockParam[]` from `@anthropic-ai/sdk` into an agent SDK entry point (e.g. `userMessageContent`) fails with a type error like:

```
Type 'ContentBlockParam' is not assignable to type 'ContentBlockParam'.
Type 'ToolReferenceBlockParam' is not assignable to type 'ContentBlockParam'.
```

The two `ContentBlockParam` types come from different copies of `@anthropic-ai/sdk` — the hoisted 0.82.0 (which includes `ToolReferenceBlockParam`) and the agent SDK's bundled 0.74.x types (which don't).

## Root Cause

`claude-agent-sdk` declares `"@anthropic-ai/sdk": "^0.74.0"` in its dependencies but its bundled `.d.ts` files import types from `@anthropic-ai/sdk`. When npm hoists a newer version (0.82.0) that has added members to union types like `ContentBlockParam`, the two type sets become structurally incompatible.

## Workaround

Pin `@anthropic-ai/sdk` to `^0.81.0` (or whichever version the agent SDK was last tested against) and use an npm override to prevent a newer version from being hoisted.

## Related Issues

- #179 — Missing dependency on `@anthropic-ai/sdk`
- #121 — Missing `@anthropic-ai/sdk` dependency causes types to resolve as `any`
- anthropics/anthropic-sdk-typescript#864 — Cross-repo duplicate

## Suggested Fix

Either:
1. Re-export the base SDK types that consumers commonly need (`Anthropic`, `APIError`, `ContentBlockParam`, `Model`, etc.) from `claude-agent-sdk` so consumers don't need a separate direct dependency
2. Or tighten the `@anthropic-ai/sdk` peer/dependency range so breaking type additions are caught at install time