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/router.go

@@ -13,6 +13,7 @@ import (
 
 	"git.yeij.top/AskaEth/Cyrene_v2/services/ai-core/model"
 	"git.yeij.top/AskaEth/Cyrene_v2/services/gateway/store"
+	"git.yeij.top/AskaEth/Cyrene_v2/services/rag"
 )
 
 // --- Interfaces for injected services ---
@@ -96,6 +97,14 @@ type VisionAnalyzer interface {
 	AnalyzeImage(ctx context.Context, prompt, imageRef string) (string, error)
 }
 
+// KnowledgeStorer manages the knowledge base.
+type KnowledgeStorer interface {
+	Ingest(ctx context.Context, userID, title, content string) (*rag.Document, error)
+	Search(ctx context.Context, userID, query string, topK int) ([]rag.Document, error)
+	List(ctx context.Context, userID string, limit int) ([]rag.Document, error)
+	Delete(ctx context.Context, userID string, id int64) error
+}
+
 // ChatStorer persists chat sessions and messages.
 type ChatStorer interface {
 	CreateSession(ctx context.Context, id, userID, title string) (*store.Session, error)
@@ -123,6 +132,7 @@ type Dependencies struct {
 	AutomationEng AutomationEngine
 	Reminders    *ReminderStore
 	Vision       VisionAnalyzer
+	Knowledge    KnowledgeStorer
 	PluginList   []map[string]string
 }
 
@@ -184,6 +194,11 @@ func (r *Router) setupRoutes() {
 	// Message search & session export
 	r.mux.HandleFunc("/api/v1/messages/search", r.authMW(r.messageSearchHandler))
 
+	// Knowledge base
+	r.mux.HandleFunc("/api/v1/knowledge/docs", r.authMW(r.knowledgeDocsHandler))
+	r.mux.HandleFunc("/api/v1/knowledge/docs/", r.authMW(r.knowledgeDocItemHandler))
+	r.mux.HandleFunc("/api/v1/knowledge/search", r.authMW(r.knowledgeSearchHandler))
+
 	// Image analysis
 	r.mux.HandleFunc("/api/v1/images/analyze", r.authMW(r.imageAnalyzeHandler))