fix: quick deploy duplicate detection, logout UX, backup toggle, CSP, SSE guard, and migration

- Detect existing projects with same image on quick deploy; show conflict dialog with options
- Move logout button to sidebar header as icon-only
- Replace backup checkbox with ToggleSwitch component
- Allow unsafe-inline in CSP script-src for SvelteKit hydration
- Guard SSE connection behind isAuthenticated() check
- Add notification_url ALTER TABLE migration for existing databases
- Restore RegisterPersistentLogger on event bus

web/src/lib/i18n/en.json

@@ -223,7 +223,11 @@
     "noImages": "No images found",
     "loadingImages": "Loading...",
     "imageLoadFailed": "Failed to load images",
-    "lowercaseHint": "Lowercase with hyphens"
+    "lowercaseHint": "Lowercase with hyphens",
+    "imageAlreadyExists": "Image already deployed",
+    "conflictDescription": "A project using this image already exists. You can open the existing project to deploy a new version, or create a separate project.",
+    "openProject": "Open project \u2192",
+    "createNewAnyway": "Create New Project"
   },
   "settings": {
     "title": "Settings",