feat(rag): pgvector knowledge base with API and LLM tools

- services/rag: knowledge_docs store — vector search via the shared
  embedder (HNSW index, graceful ILIKE fallback), list/delete scoped to
  the user, search intentionally global for the single-user deployment
- gateway: GET/POST /knowledge/docs, DELETE /knowledge/docs/:id,
  POST /knowledge/search
- plugins/knowledge: knowledge_search and knowledge_ingest tools so the
  persona can save and recall information mid-conversation
- main: migrations, store wiring, plugin registration

backend/services/gateway/api/handlers_more.go

@@ -258,8 +258,7 @@ func (r *Router) sessionExportHandler(w http.ResponseWriter, req *http.Request)
 	}
 }
 
-func (r *Router) imageAnalyzeHandler(w http.ResponseWriter, req *http.Request) {
-	if req.Method != "POST" { writeJSON(w, 405, M{"error": "POST required"}); return }
+func (r *Router) imageAnalyzeHandler(w http.ResponseWriter, req *http.Request) {	if req.Method != "POST" { writeJSON(w, 405, M{"error": "POST required"}); return }
 	if r.deps.Vision == nil { writeJSON(w, 503, M{"error": "vision not available"}); return }
 	var body struct {
 		ImageURL    string `json:"image_url"`
@@ -305,3 +304,58 @@ func (r *Router) hostExecHandler(w http.ResponseWriter, req *http.Request) {
 		"command": body.Command,
 	})
 }
+
+// ===== Knowledge Base =====
+
+func (r *Router) knowledgeDocsHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.Knowledge == nil { writeJSON(w, 503, M{"error": "knowledge base unavailable"}); return }
+	uid := r.userID(req)
+	switch req.Method {
+	case "GET":
+		docs, err := r.deps.Knowledge.List(req.Context(), uid, 50)
+		if err != nil { writeJSON(w, 500, M{"error": err.Error()}); return }
+		writeJSON(w, 200, M{"docs": docs})
+	case "POST":
+		var body struct {
+			Title   string `json:"title"`
+			Content string `json:"content"`
+		}
+		json.NewDecoder(req.Body).Decode(&body)
+		if body.Content == "" { writeJSON(w, 400, M{"error": "missing content"}); return }
+		doc, err := r.deps.Knowledge.Ingest(req.Context(), uid, body.Title, body.Content)
+		if err != nil { writeJSON(w, 500, M{"error": err.Error()}); return }
+		writeJSON(w, 201, M{"doc": doc})
+	default:
+		writeJSON(w, 405, M{"error": "method not allowed"})
+	}
+}
+
+func (r *Router) knowledgeDocItemHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.Knowledge == nil { writeJSON(w, 503, M{"error": "knowledge base unavailable"}); return }
+	if req.Method != "DELETE" { writeJSON(w, 405, M{"error": "method not allowed"}); return }
+	idStr := strings.TrimPrefix(req.URL.Path, "/api/v1/knowledge/docs/")
+	var id int64
+	if _, err := fmt.Sscanf(idStr, "%d", &id); err != nil || id <= 0 {
+		writeJSON(w, 400, M{"error": "invalid id"})
+		return
+	}
+	if err := r.deps.Knowledge.Delete(req.Context(), r.userID(req), id); err != nil {
+		writeJSON(w, 404, M{"error": err.Error()})
+		return
+	}
+	writeJSON(w, 204, nil)
+}
+
+func (r *Router) knowledgeSearchHandler(w http.ResponseWriter, req *http.Request) {
+	if r.deps.Knowledge == nil { writeJSON(w, 503, M{"error": "knowledge base unavailable"}); return }
+	if req.Method != "POST" { writeJSON(w, 405, M{"error": "POST required"}); return }
+	var body struct {
+		Query string `json:"query"`
+		TopK  int    `json:"top_k"`
+	}
+	json.NewDecoder(req.Body).Decode(&body)
+	if body.Query == "" { writeJSON(w, 400, M{"error": "missing query"}); return }
+	docs, err := r.deps.Knowledge.Search(req.Context(), r.userID(req), body.Query, body.TopK)
+	if err != nil { writeJSON(w, 500, M{"error": err.Error()}); return }
+	writeJSON(w, 200, M{"docs": docs, "total": len(docs)})
+}