Fix template variable docs to match actual notifier output

Audit and fix all template variable references:
- template_vars.py: Add missing fields (album_id, old_shared,
  new_shared, latitude, longitude, owner_id, people per asset)
- _SAMPLE_CONTEXT: Use proper structured data matching
  build_asset_detail() output (id, owner_id, latitude, longitude,
  people per asset, playback_url for videos)
- i18n: Fix all variable descriptions for accuracy, add missing
  fields, mark scheduler-dependent slots as "not yet implemented"
- Variables modal: Add album_fields section for periodic_summary
- Shared _ASSET_FIELDS and _ALBUM_FIELDS dicts in template_vars.py
  to keep scheduled/memory slots DRY

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/i18n/en.json

@@ -268,6 +268,7 @@
 		"preview": "Preview",
 		"variables": "Variables",
 		"assetFields": "Asset fields (in {% for asset in added_assets %})",
+		"albumFields": "Album fields (in {% for album in albums %})",
 		"confirmDelete": "Delete this template config?"
 	},
 	"templateVars": {
@@ -275,38 +276,50 @@
 		"message_assets_removed": { "description": "Notification when assets are removed from an album" },
 		"message_album_renamed": { "description": "Notification when an album is renamed" },
 		"message_album_deleted": { "description": "Notification when an album is deleted" },
-		"periodic_summary_message": { "description": "Periodic album summary with stats" },
-		"scheduled_assets_message": { "description": "Scheduled asset picks from albums" },
-		"memory_mode_message": { "description": "\"On This Day\" memories from past years" },
+		"periodic_summary_message": { "description": "Periodic album summary (scheduler not yet implemented)" },
+		"scheduled_assets_message": { "description": "Scheduled asset delivery (scheduler not yet implemented)" },
+		"memory_mode_message": { "description": "\"On This Day\" memories (scheduler not yet implemented)" },
+		"album_id": "Album ID (UUID)",
 		"album_name": "Album name",
-		"album_url": "Public share URL (if available)",
+		"album_url": "Public share URL (empty if not shared)",
 		"added_count": "Number of assets added",
 		"removed_count": "Number of assets removed",
-		"change_type": "Type of change",
-		"people": "Detected people names (use {{ people | join(', ') }})",
-		"added_assets": "List of added asset objects (use {% for asset in added_assets %})",
-		"removed_assets": "List of removed asset IDs",
-		"shared": "Whether album is shared (true/false)",
-		"video_warning": "Video size warning text",
-		"old_name": "Previous album name",
-		"new_name": "New album name",
-		"albums": "List of album objects (use {% for album in albums %})",
-		"assets": "List of asset objects (use {% for asset in assets %})",
-		"date": "Current date/time",
+		"change_type": "Type of change (assets_added, assets_removed, album_renamed, album_deleted)",
+		"people": "Detected people names (list, use {{ people | join(', ') }})",
+		"added_assets": "List of asset dicts (use {% for asset in added_assets %})",
+		"removed_assets": "List of removed asset IDs (strings)",
+		"shared": "Whether album is shared (boolean)",
+		"video_warning": "Video size warning (from template config, only if videos present)",
+		"old_name": "Previous album name (rename events)",
+		"new_name": "New album name (rename events)",
+		"old_shared": "Was album shared before rename (boolean)",
+		"new_shared": "Is album shared after rename (boolean)",
+		"albums": "List of album dicts (use {% for album in albums %})",
+		"assets": "List of asset dicts (use {% for asset in assets %})",
+		"date": "Current date string",
+		"asset_id": "Asset ID (UUID)",
 		"asset_filename": "Original filename",
 		"asset_type": "IMAGE or VIDEO",
 		"asset_created_at": "Creation date/time (ISO 8601)",
 		"asset_owner": "Owner display name",
+		"asset_owner_id": "Owner user ID",
 		"asset_description": "User or EXIF description",
-		"asset_url": "Public viewer URL",
-		"asset_download_url": "Direct download URL",
-		"asset_photo_url": "Preview image URL (images only)",
-		"asset_playback_url": "Video playback URL (videos only)",
-		"asset_is_favorite": "Whether asset is favorited",
+		"asset_people": "People detected in this asset (list)",
+		"asset_is_favorite": "Whether asset is favorited (boolean)",
 		"asset_rating": "Star rating (1-5 or null)",
+		"asset_latitude": "GPS latitude (float or null)",
+		"asset_longitude": "GPS longitude (float or null)",
 		"asset_city": "City name",
 		"asset_state": "State/region name",
-		"asset_country": "Country name"
+		"asset_country": "Country name",
+		"asset_url": "Public viewer URL (if shared)",
+		"asset_download_url": "Direct download URL (if shared)",
+		"asset_photo_url": "Preview image URL (images only, if shared)",
+		"asset_playback_url": "Video playback URL (videos only, if shared)",
+		"album_name_field": "Album name (in album list)",
+		"album_asset_count": "Total assets in album",
+		"album_url_field": "Album share URL",
+		"album_shared": "Whether album is shared"
 	},
 	"hints": {
 		"periodicSummary": "Sends a scheduled summary of all tracked albums at specified times. Great for daily/weekly digests.",