feat(server): wire rag_platform components to app.state lifespan

Initialize in lifespan() (after bitable, before yield):
- KBStore + ensure_tables() → app.state.kb_store (if database_url available)
- RetrievalEngine + vector_store → app.state.retrieval_engine (if database_url available)
- HitProcessor → app.state.hit_processor (with llm_gateway)
- TaskManager → app.state.task_manager (degraded mode, InMemoryTaskStore)
- KBSettingsStore → app.state.kb_settings_store (singleton)

Each component wrapped in try/except — failures logged but don't block startup.
Follows same pattern as episodic memory initialization.

src/agentkit/server/app.py

@@ -440,6 +440,84 @@ async def lifespan(app: FastAPI):
     except Exception:
         logger.exception("Failed to initialize bitable subsystem")
 
+    # RAG platform subsystem (P1): wire KBStore, RetrievalEngine, HitProcessor,
+    # TaskManager, KBSettingsStore into app.state. Each component is initialized
+    # independently so failures don't block app startup. KBStore + RetrievalEngine
+    # require database_url (PostgreSQL + pgvector); the rest work in degraded mode.
+    rag_database_url = None
+    if server_config and hasattr(server_config, "memory") and server_config.memory:
+        rag_database_url = server_config.memory.get("episodic", {}).get("database_url")
+    rag_database_url = rag_database_url or os.environ.get("DATABASE_URL")
+
+    if rag_database_url:
+        try:
+            from agentkit.rag_platform.store import create_session_factory
+
+            kb_session_factory = create_session_factory(rag_database_url)
+
+            # Ensure rag_platform tables exist (idempotent, async)
+            try:
+                from agentkit.rag_platform.store import ensure_tables
+
+                await ensure_tables(rag_database_url)
+            except Exception:
+                logger.exception("Failed to ensure rag_platform tables")
+
+            # KBStore — KB/Document persistence
+            try:
+                from agentkit.rag_platform.store import KBStore
+
+                app.state.kb_store = KBStore(session_factory=kb_session_factory)
+                logger.info("KBStore initialized")
+            except Exception:
+                logger.exception("Failed to initialize KBStore")
+
+            # RetrievalEngine — requires llama_index PGVectorStore
+            try:
+                from agentkit.rag_platform.indexing import create_vector_store
+                from agentkit.rag_platform.retrieval import RetrievalEngine
+
+                vector_store = create_vector_store(rag_database_url)
+                app.state.vector_store = vector_store
+                app.state.retrieval_engine = RetrievalEngine(
+                    vector_store=vector_store,
+                    session_factory=kb_session_factory,
+                )
+                logger.info("RetrievalEngine initialized (pgvector ready)")
+            except Exception:
+                logger.exception("Failed to initialize RetrievalEngine — vector search unavailable")
+        except Exception:
+            logger.exception("Failed to initialize rag_platform DB components")
+
+    # HitProcessor — LLM-based answer generation from retrieval results
+    try:
+        from agentkit.rag_platform.hit_processing import HitProcessor
+
+        app.state.hit_processor = HitProcessor(llm_gateway=app.state.llm_gateway)
+        logger.info("HitProcessor initialized")
+    except Exception:
+        logger.exception("Failed to initialize HitProcessor")
+
+    # TaskManager — async vectorize/batch-index tasks
+    # ponytail: degraded mode — InMemoryTaskStore, no TaskIQ broker.
+    # Upgrade path: create_broker(redis_url) + worker process when Redis configured.
+    try:
+        from agentkit.rag_platform.tasks import TaskManager
+
+        app.state.task_manager = TaskManager()
+        logger.info("TaskManager initialized (degraded mode: InMemoryTaskStore)")
+    except Exception:
+        logger.exception("Failed to initialize TaskManager")
+
+    # KBSettingsStore — per-KB retrieval/hit-processing defaults (process singleton)
+    try:
+        from agentkit.rag_platform.settings import get_settings_store
+
+        app.state.kb_settings_store = get_settings_store()
+        logger.info("KBSettingsStore initialized")
+    except Exception:
+        logger.exception("Failed to initialize KBSettingsStore")
+
     yield
 
     # Shutdown