### Summary
As title
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
- [x] Bug Fix (non-breaking change which fixes an issue)
## Summary
Add the Go implementation of `POST
/api/v1/datasets/{dataset_id}/documents/{document_id}/chunks`.
This wires the full create-chunk path in Go:
- router and handler registration
- request/response structs
- chunk creation service logic
- embedding generation
- chunk insert into doc engine
- chunk/token counter increment
- `tag_feas` validation
- `image_base64` decoding and chunk image storage/merge
- unit tests for handler and service
## Testing
Unit tests:
- `/usr/local/go/bin/go test ./internal/handler`
- `/usr/local/go/bin/go test ./internal/service/chunk`
- `/usr/local/go/bin/go test ./internal/service`
- `/usr/local/go/bin/go test ./...`
All passed locally.
Manual curl checks:
- basic text chunk: Go passed
- chunk with `important_keywords` / `questions` / `tag_kwd` /
`tag_feas`: Go passed
- blank content validation: Go matched expected `code=102`
- invalid `image_base64` validation: Go matched expected `code=102`
- image upload and repeated image upload / merge path: Go passed twice
### What problem does this PR solve?
Implement:
1. `/api/v1/datasets/<dataset_id>/documents/<document_id>/chunks GET`
2.
`/api/v1/datasets/<dataset_id>/documents/<document_id>/chunks/<chunk_id>
PATCH`
3. `/api/v1/datasets/<dataset_id>/documents/<document_id>/chunks PATCH`
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
## Summary
Stabilizes the Go unit-test surface so the test suite can run reliably
in CI and locally via \`bash build.sh --test\`.
## Verification
\`\`\`bash
bash build.sh --test -- -count=10 -run TestWithCancel_SequentialAgent
./internal/harness/core/
bash build.sh --test -- -count=5 -run TestSiliconflowChatExtracts
./internal/entity/models/
bash build.sh --test # full suite
\`\`\`
All previously failing packages (\`admin\`, \`cli\`, \`handler\`,
\`parser\`,
\`router\`, \`service\`, \`service/chunk\`) now build and test
successfully.
\`TestWithCancel_SequentialAgent\` passes 10/10 (was flaky). SiliconFlow
reasoning test passes after switching the assertion to the SiliconFlow
wire
format.
---------
Co-authored-by: Claude <noreply@anthropic.com>
Implements POST /api/v1/searchbots/ask in Go with streaming SSE,
citations, and think-tag processing. 23 files, 90+ unit tests.
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
