feat(i18n): translate remaining components (HU/EN/DE)

Feed, VideoCard, Sidebar, PlayerModal, Channels, Stats, SettingsPanel,
OnboardingWizard, NotificationCenter, Toaster, ErrorBoundary and the relativeTime
helper are now fully translated in Hungarian, English and German, each with its own
locale area file (auto-loaded). Key parity verified across all three languages.

frontend/src/i18n/locales/en/settings.json

@@ -0,0 +1,101 @@
+{
+  "title": "Settings",
+  "tabs": {
+    "appearance": "Appearance",
+    "notifications": "Notifications",
+    "sync": "Sync",
+    "account": "Account"
+  },
+  "appearance": {
+    "colorScheme": "Color scheme",
+    "display": "Display",
+    "darkMode": "Dark mode",
+    "listView": "List view",
+    "listViewHint": "Show the feed as a compact list instead of a grid of cards.",
+    "performanceMode": "Performance mode",
+    "performanceModeHint": "Turns off the translucent glass blur and soft shadows for snappier rendering on slower machines.",
+    "showHints": "Show hints",
+    "showHintsHint": "These little hover explanations. Turn them off once you know your way around.",
+    "textSize": "Text size"
+  },
+  "notifications": {
+    "title": "Notifications",
+    "sound": "Sound on alerts",
+    "soundHint": "Play a short tone when a notification needs your attention (e.g. errors, prompts).",
+    "autoDismiss": "Auto-dismiss toasts",
+    "autoDismissHint": "When off, pop-up toasts stay until you close them. When on, they fade after the set time.",
+    "dismissAfter": "Dismiss after",
+    "sendTest": "Send a test notification",
+    "testTitle": "Test notification",
+    "testMessage": "This is what a notification looks like."
+  },
+  "sync": {
+    "myStatus": "My sync status",
+    "channels": "Channels",
+    "channelsHint": "How many channels you're subscribed to.",
+    "recentSynced": "Recent synced",
+    "recentSyncedHint": "Channels whose recent uploads (~last year) are already in the local database, so they show in your feed.",
+    "fullHistory": "Full history",
+    "fullHistoryHint": "Channels whose entire back-catalog has been fetched, out of the ones you've requested full history for (opt in per channel on the Channels page).",
+    "fullHistoryEta": "Full history ETA",
+    "fullHistoryEtaHint": "Rough estimate to finish full-history backfill of {{count}} pending channel(s), based on the shared daily quota.",
+    "myVideos": "My videos",
+    "myVideosHint": "Total videos available to you across your subscribed channels.",
+    "quotaLeft": "Quota left today",
+    "quotaLeftHint": "Shared YouTube API budget remaining today (resets midnight US Pacific). Backfill yields to it.",
+    "loading": "Loading…",
+    "apiUsage": "Your API usage",
+    "today": "Today",
+    "todayHint": "YouTube API units your own actions used today (resets midnight US Pacific). Background sync isn't counted here.",
+    "last7d": "Last 7 days",
+    "last30d": "Last 30 days",
+    "allTime": "All time",
+    "byAction": "By action (30d)",
+    "noUsage": "No usage yet.",
+    "actions": "Actions",
+    "syncSubscriptions": "Sync subscriptions",
+    "syncSubscriptionsHint": "Re-import your YouTube subscriptions and pull in any newly-followed channels.",
+    "backfillEverything": "Backfill everything",
+    "backfillEverythingHint": "Request full back-catalog backfill for every channel you're subscribed to. Older videos + complete search fill in as the shared daily quota allows.",
+    "synced": "Synced {{count}} subscriptions",
+    "syncFailed": "Sync failed",
+    "fullHistoryRequested": "Full history requested for {{count}} channels",
+    "fullHistoryFailed": "Couldn't request full history",
+    "admin": "Admin",
+    "adminPauseHint": "Pause or resume the background sync for the whole app (all users).",
+    "resumeBackgroundSync": "Resume background sync",
+    "pauseBackgroundSync": "Pause background sync"
+  },
+  "account": {
+    "title": "Account",
+    "youtubeAccess": "YouTube access",
+    "youtubeAccessIntro": "Sign-in only shares your name and email. YouTube access is granted separately, below — each is optional and revocable anytime in your Google Account.",
+    "readTitle": "Read subscriptions (your feed)",
+    "readGrantedHint": "Granted. Siftlode reads the channels you follow to build your feed. It never changes your YouTube account with this.",
+    "readEnableHint": "Read-only access to your subscriptions — required to build your feed. Siftlode can't modify anything with it.",
+    "writeTitle": "Unsubscribe (write)",
+    "writeGrantedHint": "Granted. You can unsubscribe from channels on YouTube from inside Siftlode. It only writes when you ask it to.",
+    "writeEnableHint": "Lets Siftlode unsubscribe from channels on YouTube for you. Optional — skip it to stay read-only.",
+    "granted": "Granted",
+    "enable": "Enable",
+    "enableHint": "Redirects to Google to grant the permission. Google shows an 'unverified app' notice — that's expected; click Advanced → Go to Siftlode.",
+    "walkMeThrough": "Walk me through setup"
+  },
+  "invites": {
+    "title": "Access requests",
+    "noPending": "No pending requests.",
+    "addPlaceholder": "Add an email directly…",
+    "add": "Add",
+    "decided": "{{count}} decided",
+    "approved": "Approved — they can sign in now",
+    "approveFailed": "Approve failed",
+    "denyFailed": "Deny failed",
+    "addedToWhitelist": "Added to the whitelist",
+    "addFailed": "Couldn't add that email",
+    "requested": "requested {{time}}",
+    "approveHint": "Approve — whitelist this email and email them they're in.",
+    "approve": "Approve",
+    "denyHint": "Deny this request.",
+    "deny": "Deny"
+  }
+}