Fix canned_responses 500: add missing SQL migration

The canned_responses table was registered in autoMigrate() (app.go) but
autoMigrate() is never called on the serve path (Bootstrap -> NewDatabase
-> RunMigrations only). With no SQL migration file, the table never
existed, so POST /api/v1/accounts/:id/canned_responses failed with
'relation does not exist' -> 500.

Add migration 000049 to create the table matching the GORM model
(id, account_id, content, short_code, timestamps) with the account+
short_code partial unique index and deleted_at index.

Also include two related fixes staged in the working tree:
- router.go: register notifications.GET("") alongside GET("/") to avoid
  Gin 301 trailing-slash redirect that the Vite proxy doesn't follow
- notifications/actions.js: stop the infinite loader on fetch error to
  prevent IntersectionObserver re-fire loop

backend/internal/router/router.go

@@ -1732,6 +1732,11 @@ func registerV1Routes(g *gin.RouterGroup, h *Handlers) {
 			// Notifications — account-scoped Chatwoot routes used by the dashboard frontend.
 			notifications := accountScoped.Group("/notifications")
 			{
+				// Register both "" and "/" so Gin does not 301-redirect between them.
+				// The dashboard frontend requests /notifications (no trailing slash);
+				// without the "" route Gin's RedirectTrailingSlash emits a 301 that
+				// the Vite dev proxy does not follow, causing an infinite-load loop.
+				notifications.GET("", h.Notification.List)
 				notifications.GET("/", h.Notification.List)
 				notifications.POST("/read_all", h.Notification.MarkAllRead)
 				notifications.GET("/unread_count", h.Notification.UnreadCount)

backend/migrations/000049_add_canned_responses_table.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS canned_responses;

backend/migrations/000049_add_canned_responses_table.up.sql

@@ -0,0 +1,12 @@
+CREATE TABLE IF NOT EXISTS canned_responses (
+    id SERIAL PRIMARY KEY,
+    account_id INTEGER NOT NULL,
+    content TEXT NOT NULL,
+    short_code VARCHAR(255) NOT NULL,
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW(),
+    deleted_at TIMESTAMPTZ
+);
+CREATE INDEX IF NOT EXISTS idx_canned_responses_account_id ON canned_responses(account_id);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_canned_short_code ON canned_responses(account_id, short_code) WHERE deleted_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_canned_responses_deleted_at ON canned_responses(deleted_at);

frontend/app/javascript/dashboard/store/modules/notifications/actions.js

@@ -39,6 +39,10 @@ export const actions = {
       }
     } catch (error) {
       commit(types.SET_NOTIFICATIONS_UI_FLAG, { isFetching: false });
+      // On error, stop the infinite loader — otherwise IntersectionObserver
+      // keeps firing loadMoreNotifications, incrementing page forever and
+      // re-issuing the failing request in a tight loop.
+      commit(types.SET_ALL_NOTIFICATIONS_LOADED);
     }
   },
   unReadCount: async ({ commit } = {}) => {