feat: Auto-adjust chunk recall weights based on user feedback (#12689)

### What problem does this PR solve?

Implements automatic adjustment of knowledge base chunk recall weights
based on user feedback (upvotes/downvotes). When users upvote or
downvote a response, the system locates the corresponding knowledge
snippets and adjusts their recall weight to improve future retrieval
quality.

**Closes #12670**

**How it works:**
1. User upvotes/downvotes a response via `POST /thumbup`
2. System extracts chunk IDs from the conversation reference
3. For each referenced chunk:
   - Reads current `pagerank_fea` value from document store
   - Increments (+1) for upvote or decrements (-1) for downvote
   - Clamps weight to [0, 100] range
   - Updates chunk in ES/Infinity/OceanBase
4. Future retrievals score these chunks higher/lower based on
accumulated feedback

**Files changed:**
- `api/db/services/chunk_feedback_service.py` - New service for updating
chunk pagerank weights
- `api/apps/conversation_app.py` - Integrated feedback service into
thumbup endpoint
- `test/testcases/test_web_api/test_chunk_feedback/` - Unit tests

### Type of change

- [x] New Feature (non-breaking change which adds functionality)


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Chat message feedback now updates per-chunk relevance weights
(feature-flag gated), with configurable weighting and atomic updates
across storage backends.

* **Bug Fixes**
* Stricter validation for message feedback inputs and more robust
handling of feedback transitions.

* **Tests**
* Expanded test coverage for chunk-feedback behavior, weighting
strategies, storage backends, and thumb-flip scenarios.

* **Chores**
  * CI workflow extended to run the new chunk-feedback web API tests.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: mkdev11 <YOUR_GITHUB_ID+MkDev11@users.noreply.github.com>
Co-authored-by: mkdev11 <MkDev11@users.noreply.github.com>

.github/workflows/tests.yml

@@ -247,7 +247,7 @@ jobs:
             echo "Waiting for service to be available... (last exit code: $?)"
             sleep 5
           done
-          source .venv/bin/activate && set -o pipefail; DOC_ENGINE=infinity pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_web_api/test_api_app 2>&1 | tee infinity_web_api_test.log
+          source .venv/bin/activate && set -o pipefail; DOC_ENGINE=infinity pytest -s --tb=short --level=${HTTP_API_TEST_LEVEL} test/testcases/test_web_api/test_api_app test/testcases/test_web_api/test_chunk_feedback 2>&1 | tee infinity_web_api_test.log
 
       - name: Run http api tests against Infinity
         run: |