feat(cache): thumbhash-validated asset cache + settings UX overhaul

Cache engine:
- TelegramFileCache: configurable max_entries (LRU cap applies in both TTL
  and thumbhash modes), ttl_seconds<=0 disables TTL, stats() method.
- Dispatcher builds an asset.id -> thumbhash resolver from event.added_assets
  (Immich populates thumbhash in extra) and passes it to TelegramClient, so
  asset-cache entries invalidate on visual change rather than age.
- Watcher wires app settings into cache init: URL cache = TTL + LRU cap,
  asset cache = thumbhash + LRU cap. Adds soft-reset (in-memory only) used
  when cache params change.

Settings:
- New key telegram_asset_cache_max_entries (default 5000).
- telegram_cache_ttl_hours default bumped 48 -> 720 (30d); now URL-only.
- PUT /settings resets in-memory caches when cache keys change (files kept).
- New endpoints: GET/POST /settings/telegram-cache/stats and /clear.

Settings page:
- Cache stats card (count + size + oldest/newest per bucket) with a hint
  explaining that the size is cumulative uploaded-to-Telegram bytes.
- Clear-cache button behind a confirm modal.
- New TimezoneSelector + LocaleSelector components replace raw inputs.
- max-entries input, TTL range updated (0..8760, 0 = disabled).

Mobile nav:
- "More" panel now mirrors the full sidebar tree (groups + subnodes) so
  every destination is reachable on mobile; previously flat hand-picked list.
- Nav height uses env(safe-area-inset-bottom); panel bottom + z-index fixed
  so content can't visually overlay the bottom bar.

A11y / DOM warnings:
- Password-change form has a hidden username field for password-manager
  association; autocomplete hints on all three password inputs.
- Telegram webhook secret wrapped in a no-op form + autocomplete=off.

Bug fix:
- update_settings used any(await ... for ...) which raised TypeError at
  runtime (async generator not an iterator); replaced with explicit loop.

frontend/src/lib/i18n/en.json

@@ -671,13 +671,29 @@
 		"telegram": "Telegram",
 		"webhookSecret": "Webhook Secret",
 		"webhookSecretHint": "Secret token to verify webhook requests from Telegram",
-		"cacheTtl": "Media Cache TTL (hours)",
-		"cacheTtlHint": "How long to cache uploaded Telegram file_ids before re-uploading",
+		"cacheTtl": "URL Cache TTL (hours)",
+		"cacheTtlHint": "How long to keep URL-keyed Telegram file_ids (e.g. shared links). Set 0 to disable TTL. The asset cache uses content hashing (thumbhash) and ignores this.",
+		"cacheMaxEntries": "Cache Max Entries",
+		"cacheMaxEntriesHint": "Upper bound per cache (URL and asset). Oldest entries are evicted first (LRU). Default 5000.",
+		"cacheStats": "Cache contents",
+		"cacheStatsHint": "Size shown is the total bytes of media originally uploaded to Telegram for cached entries — i.e. approximate re-upload bandwidth the cache is saving. The cache file itself is only a few KB; the media lives on Telegram's servers.",
+		"cacheStatsUrl": "URL cache",
+		"cacheStatsAsset": "Asset cache",
+		"cacheStatsEntries": "entries",
+		"cacheStatsEmpty": "empty",
+		"cacheStatsOldest": "oldest",
+		"cacheStatsNewest": "newest",
+		"clearCache": "Clear Media Cache",
+		"clearCacheHint": "Delete cached Telegram file_ids. Next send will re-upload media.",
+		"clearCacheConfirmTitle": "Clear Telegram cache?",
+		"clearCacheConfirm": "This removes all cached Telegram file_ids. Subsequent notifications will re-upload media, which may take longer and use more bandwidth.",
+		"clearCacheConfirmBtn": "Clear cache",
+		"clearCacheDone": "Telegram cache cleared",
 		"timezone": "Timezone",
 		"timezoneHint": "IANA timezone (e.g. UTC, Europe/Warsaw, America/New_York). Used to interpret HH:MM fields like quiet hours.",
 		"locales": "Template Languages",
 		"supportedLocales": "Supported Locales",
-		"supportedLocalesHint": "Comma-separated locale codes for template editing (e.g. en,ru,de,fr)",
+		"supportedLocalesHint": "Languages available when authoring notification and command templates. Built-in defaults ship for English and Russian; other languages start empty.",
 		"saved": "Settings saved"
 	},
 	"hints": {
@@ -813,6 +829,29 @@
 		"showDetails": "Show details",
 		"hideDetails": "Hide details"
 	},
+	"timezone": {
+		"searchPlaceholder": "Search cities or IANA codes…",
+		"detect": "Detect",
+		"utc": "UTC",
+		"noMatches": "No timezones match"
+	},
+	"locales": {
+		"empty": "No languages selected. Add one below to start authoring templates.",
+		"add": "Add language",
+		"searchPlaceholder": "Search or type a code (e.g. de-CH)…",
+		"addCustom": "Add custom code",
+		"noSuggestions": "No matches. Type a valid locale code (2–3 letters).",
+		"primary": "Primary",
+		"shipped": "Built-in",
+		"shippedHint": "Default notification & command templates ship for this language.",
+		"makePrimary": "Make primary",
+		"moveUp": "Move up",
+		"moveDown": "Move down",
+		"remove": "Remove",
+		"removeLast": "At least one language is required",
+		"reorder": "Drag to reorder",
+		"orderHint": "First language is the primary fallback when a translation is missing. Drag to reorder."
+	},
 	"snack": {
 		"eventsCleared": "{count} event(s) cleared",
 		"providerSaved": "Provider saved",