feat: refactor volatile cache to vector storage with HybridRAG integration

- Migrate volatile backend from Redis to Qdrant for semantic search
- Add natural language conversion for structured data embedding
- Simplify API: /volatile/search, /volatile/store, /{namespace}/{key}
- Integrate volatile into HybridRAG with priority boost in RRF fusion
- Add POST /maintenance/cleanup/volatile for expiry purging
- Update tests for new Qdrant-based architecture (37/37 pass)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/models/hybrid_rag.py

@@ -14,13 +14,16 @@ class HybridRAGConfig(BaseModel):
     vector_limit: int = Field(default=10, ge=1, le=50, description="Max vector results")
     graph_limit: int = Field(default=10, ge=1, le=50, description="Max graph results")
     web_limit: int = Field(default=5, ge=1, le=20, description="Max web results")
+    volatile_limit: int = Field(default=1, ge=1, le=5, description="Max volatile results (typically 1)")
     enable_vector: bool = Field(default=True, description="Enable vector search")
     enable_graph: bool = Field(default=True, description="Enable graph search")
     enable_web: bool = Field(default=True, description="Enable web search")
+    enable_volatile: bool = Field(default=True, description="Enable volatile cache search")
     enable_reranking: bool = Field(default=True, description="Enable LLM re-ranking")
     enable_enrichment: bool = Field(default=True, description="Enable graph enrichment")
     final_result_count: int = Field(default=10, ge=1, le=50, description="Final results to return")
     rrf_k: int = Field(default=60, ge=1, le=100, description="RRF constant")
+    volatile_threshold: float = Field(default=0.8, ge=0.5, le=1.0, description="Volatile similarity threshold")
 
 
 class RelatedDossier(BaseModel):
@@ -34,7 +37,7 @@ class RelatedDossier(BaseModel):
 
 class HybridRAGResult(BaseModel):
     """Single result from HybridRAG query."""
-    source_type: str = Field(..., description="Source: 'vector', 'graph', 'web'")
+    source_type: str = Field(..., description="Source: 'wiki', 'web', 'volatile'")
     title: str
     content: str
     url: Optional[str] = Field(None, description="URL for web results")
@@ -53,6 +56,7 @@ class TimingBreakdown(BaseModel):
     vector_ms: float = Field(..., description="Phase 1: Vector search")
     graph_ms: float = Field(..., description="Phase 1: Graph search")
     web_ms: float = Field(..., description="Phase 1: Web search")
+    volatile_ms: float = Field(default=0, description="Phase 1: Volatile cache search")
     fusion_ms: float = Field(..., description="Phase 2: RRF fusion")
     enrichment_ms: float = Field(..., description="Phase 3: Graph enrichment")
     reranking_ms: float = Field(..., description="Phase 4: LLM re-ranking")