feat(memory): add memory management page with CRUD, search, and indexing

Add full-stack memory document management:
- Backend: extend MemoryStore with admin queries (ListAllDocumentsGlobal,
  GetDocumentDetail, ListChunks), HTTP handler with auth middleware
- Frontend: memory page with agent/scope filters, document table with
  pagination, view/edit dialog with content and chunks tabs, create dialog
  with scope selection, semantic search dialog
- UI fixes: reduce input/textarea focus ring width, prevent ring clipping
  in dialog scroll containers, widen memory dialogs on desktop

cmd/gateway.go

@@ -617,6 +617,11 @@ func runGateway() {
 		server.SetPendingMessagesHandler(pendingMessagesH)
 	}
 
+	// Memory management API (wired directly, only needs MemoryStore + token)
+	if pgStores != nil && pgStores.Memory != nil {
+		server.SetMemoryHandler(httpapi.NewMemoryHandler(pgStores.Memory, cfg.Gateway.Token))
+	}
+
 	// Workspace file serving endpoint — serves files by absolute path, auth-token protected.
 	// Supports media from any agent workspace (each agent has its own workspace from DB).
 	server.SetFilesHandler(httpapi.NewFilesHandler(cfg.Gateway.Token))