Add import/export for camera group layouts and per-camera streaming settings (#24025)

* add import/export for camera group layouts and streaming settings

Camera group layouts and per-camera streaming settings are stored in the browser's IndexedDB, so they are tied to a single browser on a single device. Users with more than one device have to rebuild every group layout and re-pick every camera's stream settings by hand, and clearing browser data loses the work.

Add a Backup & Restore card to Settings > UI Settings that exports these settings to a JSON file and imports that file on another device. Import shows a confirmation dialog with per-section counts, switches for layouts, streaming settings, and UI preferences, and warnings about camera groups or cameras in the file that are not on this server.

Server-side storage is deliberately avoided. These are per-device presentation settings: a layout arranged for a desktop is wrong on a tablet, and continuous full-resolution streams that are free on a wired LAN are not on a phone. An explicit file moves settings only when the user chooses to move them.

Implementation notes:

- web/src/utils/uiSettingsTransfer.ts owns a registry of transferable IndexedDB keys. Each entry records whether the key is user-namespaced, matching which persistence hook wrote it, plus a zod schema for its value.
- Only registry-known keys are ever written, and only when their value passes that schema. The file format deliberately lets unknown keys survive parsing, so this filter is what prevents a hand-edited file from writing arbitrary storage keys or out-of-range values.
- Export falls back to the legacy un-namespaced key, because the username migration runs lazily on first mount of each owning hook.
- Streaming settings merge per group rather than replacing the whole map, so groups configured only on the receiving device survive.
- Import writes storage and then reloads, because useUserPersistence reads a key only on mount and StreamingSettingsProvider would otherwise write its stale in-memory state back over the import.
- playbackBandwidthEstimate, frigate-search-history, and live-layout are excluded: the first two are measurements and user data rather than preferences, and live-layout's default is derived from the device.

* merge imported streaming settings per camera instead of per group

web/public/locales/en/views/settings.json

@@ -179,6 +179,31 @@
       "desc": "Streaming settings for each camera group are stored in your browser's local storage.",
       "clearAll": "Clear All Streaming Settings"
     },
+    "backupRestore": {
+      "title": "Backup & Restore",
+      "transfer": {
+        "label": "Device Settings File",
+        "desc": "Camera group layouts, streaming settings, and UI preferences are stored in your browser. Export them to a file to back them up or to move them to another device.",
+        "export": "Export Settings",
+        "import": "Import Settings"
+      },
+      "importDialog": {
+        "title": "Import Settings",
+        "desc": "Choose what to apply from this file. Frigate will reload when the import finishes.",
+        "exportedFrom": "Exported {{date}} from Frigate config version {{version}}",
+        "layouts_one": "Camera group layouts ({{count}} group)",
+        "layouts_other": "Camera group layouts ({{count}} groups)",
+        "streaming_one": "Streaming settings ({{count}} camera)",
+        "streaming_other": "Streaming settings ({{count}} cameras)",
+        "preferences_one": "UI preferences ({{count}} setting)",
+        "preferences_other": "UI preferences ({{count}} settings)",
+        "unknownGroups_one": "Camera group {{groups}} is not on this server. Its settings will be saved but unused.",
+        "unknownGroups_other": "Camera groups {{groups}} are not on this server. Their settings will be saved but unused.",
+        "unknownCameras_one": "Camera {{cameras}} is not on this server. Its streaming settings will be ignored.",
+        "unknownCameras_other": "Cameras {{cameras}} are not on this server. Their streaming settings will be ignored.",
+        "confirm": "Import"
+      }
+    },
     "recordingsViewer": {
       "title": "Recordings Viewer",
       "defaultPlaybackRate": {
@@ -198,11 +223,20 @@
     "toast": {
       "success": {
         "clearStoredLayout": "Cleared stored layout for {{cameraName}}",
-        "clearStreamingSettings": "Cleared streaming settings for all camera groups."
+        "clearStreamingSettings": "Cleared streaming settings for all camera groups.",
+        "exportUiSettings": "Exported settings",
+        "importUiSettings": "Imported settings"
       },
       "error": {
         "clearStoredLayoutFailed": "Failed to clear stored layout: {{errorMessage}}",
-        "clearStreamingSettingsFailed": "Failed to clear streaming settings: {{errorMessage}}"
+        "clearStreamingSettingsFailed": "Failed to clear streaming settings: {{errorMessage}}",
+        "exportUiSettingsFailed": "Failed to export settings",
+        "importNothingToApply": "Failed to import settings: file contains no settings",
+        "importInvalidJson": "Failed to import settings: file is not valid JSON",
+        "importWrongType": "Failed to import settings: file is not a Frigate settings export",
+        "importUnsupportedVersion": "Failed to import settings: file requires a newer version of Frigate",
+        "importInvalidSchema": "Failed to import settings: file is malformed",
+        "importUiSettingsFailed": "Failed to import settings"
       }
     }
   },