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>

test/testcases/test_http_api/test_chat_assistant_management/test_chat_sdk_routes_unit.py

@@ -346,10 +346,21 @@ def _load_chat_module(monkeypatch):
         def query(**_kwargs):
             return []
 
+    user_service_mod.UserService = type("UserService", (), {})
     user_service_mod.TenantService = _StubTenantService
     user_service_mod.UserTenantService = _StubUserTenantService
     monkeypatch.setitem(sys.modules, "api.db.services.user_service", user_service_mod)
 
+    chunk_feedback_service_mod = ModuleType("api.db.services.chunk_feedback_service")
+
+    class _StubChunkFeedbackService:
+        @staticmethod
+        def apply_feedback(**_kwargs):
+            return {"success_count": 0, "fail_count": 0, "chunk_ids": []}
+
+    chunk_feedback_service_mod.ChunkFeedbackService = _StubChunkFeedbackService
+    monkeypatch.setitem(sys.modules, "api.db.services.chunk_feedback_service", chunk_feedback_service_mod)
+
     api_utils_mod = ModuleType("api.utils.api_utils")
 
     def _check_duplicate_ids(ids, label):