feat(E): Unified Search — 24 Tasks complete

- SPIKE-E: FTS+Vector+Permission benchmark on 10k records (all <30ms)
- E-PROV: supports_fts/vector/rag/graph capability flags on all providers
- E-FTS/VEC: All 11 providers refactored to BaseSearchProvider with permission filtering
- E-PERM: Over-fetch strategy for vector+permission (15x faster than ANY() filter)
- E-FUSE: rrf_fusion_multi() for N-way RRF over FTS+Vector+RAG+Graph
- E-LLM: Query understanding cleaned up to use central llm_complete()
- E-CHUNK: Document chunking module + document_chunks table with HNSW index
- E-EMB: Chunk embedding ARQ jobs (index_file_chunks, reindex_chunks)
- E-RAG: RAG retrieval via FileSearchProvider.search_rag()
- E-GRAPH: GraphRAG BFS traversal via GraphRAGSearchProvider.search_graph()
- E-IX-EVT: Auto-indexing via outbox events + delete/cleanup handlers
- E-IX-RE: Batch reindex with progress tracking + reindex_all job
- E-DATA-LIFE: Lifecycle module (remove/rebuild/restore/correct) + API endpoints
- E-K-MEM: AgentMemorySearchProvider
- E-P-AI: AIChatSearchProvider
- E-P-WF: WorkflowSearchProvider
- E-P-COMM: ConversationSearchProvider verified (already on BaseSearchProvider)
- E-API: Filter params (date_from/to, tags, sort) + /facets endpoint
- E-TOOL: unified_search AI tool registered in ToolRegistry
- E-MCP: Search tool in MCP server with normal RBAC/tenant checks
- E-UI-CMD: CommandPalette (Cmd+K) with debounced search + recent searches
- E-UI-FAC: SearchFacets, SearchResultCard, SavedSearches components
- E-TEST: 40 new tests in test_unified_search_phase_e.py (105 total green)
- E-DOC: api-documentation.md, plugin-development-guide.md, test-strategy.md updated

105 tests passing, TypeScript clean.

app/plugins/builtins/unified_search/provider_registry.py

@@ -19,6 +19,10 @@ class SearchProvider(Protocol):
     """Protocol for entity-specific search providers."""
 
     entity_type: str
+    supports_fts: bool
+    supports_vector: bool
+    supports_rag: bool
+    supports_graph: bool
 
     async def search_fts(
         self,
@@ -81,6 +85,23 @@ class SearchProviderRegistry:
         """Get all registered entity types."""
         return list(self._providers.keys())
 
+    def get_providers_by_capability(self, capability: str) -> list[SearchProvider]:
+        """Get all providers that support a given capability (fts/vector/rag/graph)."""
+        flag_attr = f"supports_{capability}"
+        return [p for p in self._providers.values() if getattr(p, flag_attr, False)]
+
+    def get_capabilities(self, entity_type: str) -> dict[str, bool]:
+        """Get capability flags for a specific entity type."""
+        provider = self.get(entity_type)
+        if provider is None:
+            return {"fts": False, "vector": False, "rag": False, "graph": False}
+        return {
+            "fts": getattr(provider, "supports_fts", False),
+            "vector": getattr(provider, "supports_vector", False),
+            "rag": getattr(provider, "supports_rag", False),
+            "graph": getattr(provider, "supports_graph", False),
+        }
+
     def clear(self) -> None:
         """Clear all registered providers."""
         self._providers.clear()
@@ -130,6 +151,15 @@ async def auto_register_providers(db: AsyncSession) -> None:
     from app.plugins.builtins.unified_search.providers.user_provider import (
         UserSearchProvider,
     )
+    from app.plugins.builtins.unified_search.providers.agent_memory_provider import (
+        AgentMemorySearchProvider,
+    )
+    from app.plugins.builtins.unified_search.providers.ai_chat_provider import (
+        AIChatSearchProvider,
+    )
+    from app.plugins.builtins.unified_search.providers.workflow_provider import (
+        WorkflowSearchProvider,
+    )
     from app.plugins.builtins.graph_rag.contracts import GraphRagContract
     GraphRAGSearchProvider = GraphRagContract.GraphRAGSearchProvider
 
@@ -148,6 +178,9 @@ async def auto_register_providers(db: AsyncSession) -> None:
         TagSearchProvider,
         ConversationSearchProvider,
         UserSearchProvider,
+        AgentMemorySearchProvider,
+        AIChatSearchProvider,
+        WorkflowSearchProvider,
         GraphRAGSearchProvider,
     ]:
         try: