fix(widget-secrets): add missing widget_secret migration and add error notifications

The widget_secret table was defined in all three Drizzle schema files but
no SQL migration was ever generated to create it, causing setSecret to
fail with 'no such table: widget_secret' in production (drizzle-kit push
in development hid the problem).

- Add migration SQL for sqlite (0040), mysql (0042), postgresql (0008)
- Update journal entries for all three dialects
- Add onError handlers to setSecret/deleteSecret mutations so errors
  are shown as red notifications instead of silently swallowed

Fixes #6186

packages/db/migrations/sqlite/0040_add_widget_secret.sql

@@ -0,0 +1,8 @@
+CREATE TABLE `widget_secret` (
+	`item_id` text NOT NULL,
+	`kind` text NOT NULL,
+	`value` text NOT NULL,
+	`updated_at` integer NOT NULL,
+	PRIMARY KEY(`item_id`, `kind`),
+	FOREIGN KEY (`item_id`) REFERENCES `item`(`id`) ON UPDATE no action ON DELETE cascade
+);

packages/db/migrations/sqlite/meta/_journal.json

@@ -281,6 +281,13 @@
       "when": 1780764500000,
       "tag": "0039_merge_custom_widget_url",
       "breakpoints": true
+    },
+    {
+      "idx": 40,
+      "version": "6",
+      "when": 1783176100870,
+      "tag": "0040_add_widget_secret",
+      "breakpoints": true
     }
   ]
 }