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/mysql/0042_add_widget_secret.sql

@@ -0,0 +1,9 @@
+CREATE TABLE `widget_secret` (
+	`item_id` varchar(64) NOT NULL,
+	`kind` varchar(64) NOT NULL,
+	`value` text NOT NULL,
+	`updated_at` timestamp NOT NULL,
+	CONSTRAINT `widget_secret_item_id_kind_pk` PRIMARY KEY(`item_id`,`kind`)
+);
+--> statement-breakpoint
+ALTER TABLE `widget_secret` ADD CONSTRAINT `widget_secret_item_id_item_id_fk` FOREIGN KEY (`item_id`) REFERENCES `item`(`id`) ON DELETE cascade ON UPDATE no action;