feat(rag): per-user annotation signals for personalized RAG retrieval (#3240)

[mrveiss]

Closes #3240

Summary

Adds per-user scoping to the RAG feedback and pattern learning system so individual user engagement (accept/reject source cards) biases retrieval for that user only, without polluting global patterns.

Changes

• retrieval_learner.py — user_id param added throughout; Redis stream key rag:feedback:{date} → rag:feedback:{uid}:{date}; pattern keys namespaced rag:retrieval_patterns:{uid}:{hash}; get_matching_pattern() uses 4-level fallback: user-exact → user-complexity-only → global-exact → global-complexity-only
• rag_service.py — user_id threaded through _store_feedback_in_stream(), _emit_ranked_feedback(), _lookup_retrieval_pattern(), _record_retrieval_outcome(), and advanced_search()
• api/knowledge_rag_feedback.py (new) — POST /knowledge_base/rag-feedback endpoint for user-scoped annotation events
• core_routers.py — registers new knowledge_rag_feedback_router
• KnowledgeResearchPanel.vue — acceptSource() and rejectSource() now call _emitAnnotationFeedback() which posts to the new endpoint with user_id from useUserStore

Tests

• retrieval_learner_user_scoped_test.py (new) — 14 tests: stream key namespacing, pattern key namespacing, user-scoped lookup, global fallback, preference of user over global, low-confidence user pattern skipping, record_pattern_outcome user scoping, end-to-end cycle
• retrieval_learner_test.py — updated cursor key assertion for new key format

Note: tests require the backend Docker container for module resolution (models.task_context import chain); environment confirmed pre-existing limitation unrelated to this PR.

[mrveiss]

Review fixes applied ✓

• Critical — _GLOBAL_USER renamed to GLOBAL_USER (public) throughout retrieval_learner.py, rag_service.py, knowledge_rag_feedback.py, and both test files
• Critical — RagFeedbackRequest gains query: str field; query_text in the Redis stream entry now stores the actual search query instead of source_url; KnowledgeResearchPanel.vue passes query.value in the POST body
• Important — deferred import moved to module-level: from knowledge.search_components.retrieval_learner import GLOBAL_USER, get_retrieval_learner
• Important — decision field typed as Literal["accepted", "rejected"] with from typing import Literal; invalid decisions now rejected at the API boundary
• Important — unused req: Request = None parameter removed from record_rag_feedback; Request import removed
• Minor — _STREAM_TTL_SECONDS = TTL_30_DAYS moved from function body to module level in rag_service.py