QueryRewrite prompt builder and response parser. Zero external
dependencies.
### Functions
- `BuildQueryRewritePrompt`: Renders `minirag_query2kwd` prompt with
query and type pool
- `ParseQueryRewriteResponse`: Parses LLM JSON response with fallback
for markdown and extra text
### Testing
```
=== RUN TestBuildQueryRewritePrompt --- PASS
=== RUN TestParseQueryRewriteResponse_ValidJSON --- PASS
=== RUN TestParseQueryRewriteResponse_MarkdownBlock --- PASS
=== RUN TestParseQueryRewriteResponse_ExtraText --- PASS
=== RUN TestParseQueryRewriteResponse_Invalid --- PASS
=== RUN TestParseQueryRewriteResponse_EmptyEntities --- PASS
```
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
