feat(notifications): dedicate AI Failure Detection notification event (#1794)

Split Obico failure-detection dispatch out of the multiplexed
  on_printer_error event onto its own on_ai_failure_detection event so
  users can subscribe to AI alerts without also enabling HMS hardware-
  error pages, and so the discoverable label "AI Failure Detection" is
  what subscribes them rather than the unrelated "Printer Error" toggle.

  New column on notification_providers (default False, branched
  SQLite/Postgres migration), new notification_service.on_ai_failure_detection
  method, new ai_failure_detection template, obico_actions._notify swap.
  Frontend gets a summary badge, a toggle row with description, and ntfy
  priority surfacing. 14 new tests pin the routing + the regression guard
  ("Printer Error" alone must NOT receive AI notifications now). 11 locales
  covered.

  Existing providers keep working: HMS hardware errors continue to ride
  on_printer_error unchanged; users who want spaghetti alerts opt in via
  the new toggle.

static/index.html

@@ -26,8 +26,8 @@
 
     <!-- Splash screens for iOS -->
     <link rel="apple-touch-startup-image" href="/img/android-chrome-512x512.png" />
-    <script type="module" crossorigin src="/assets/index-ef6eQr6-.js"></script>
-    <link rel="stylesheet" crossorigin href="/assets/index-D9kvaB_m.css">
+    <script type="module" crossorigin src="/assets/index-CksvU0PF.js"></script>
+    <link rel="stylesheet" crossorigin href="/assets/index-DNavQjwR.css">
   </head>
   <body>
     <div id="root"></div>