feat: add German and English UI language support

A single-language interface makes the app less usable for part of the audience
and encourages more hardcoded copy as new screens and states are added.
Introducing a shared i18n path with a persisted language preference gives the
UI one consistent way to present text and lowers the risk of partial or
inconsistent localization over time.

The surrounding copy cleanup belongs in the same change because it aligns
existing labels, messages, and settings text with that translation structure
instead of leaving mixed localization approaches in place.

CLAUDE.md

@@ -37,6 +37,7 @@ Renderer (React)
 ├── AppShell.tsx         — Tab routing, sidebar/main focus, global playback overlay
 ├── screens/             — FollowingScreen, BrowseScreen, CategoryScreen,
 │                          ChannelScreen (main screen), StreamListScreen, Settings, Account
+├── i18n/                — `de.ts`, `en.ts`, `useT.ts` for localized UI copy
 ├── components/
 │   ├── VideoPlayer.tsx  — hls.js <video> wrapper (forwardRef, imperative handle)
 │   ├── PlaybackOverlay.tsx — DOM overlay over the video (z-index: 300)
@@ -51,7 +52,7 @@ Renderer (React)
 │   ├── playbackKeys.ts  — Shared key dispatch for playback (AppShell + ChannelScreen)
 │   └── hlsNoCacheLoader.ts — Fetch API-based hls.js loader (cache: 'no-store')
 ├── input/gamepad.ts     — Browser Gamepad API (Windows, dev mode)
-└── context/SettingsContext.tsx — localStorage settings (streamBadgeMode, sidebarWidth, …)
+└── context/SettingsContext.tsx — localStorage settings (streamBadgeMode, sidebarWidth, language, …)
 ```
 
 ### Data Flow
@@ -146,8 +147,12 @@ src/renderer/src/
     CategoryScreen.tsx        — Streams for a category (A=direct play, X=channel page)
     ChannelScreen.tsx         — Channel detail, VOD shelf, VideoPlayer + PlaybackOverlay, chapter panel, quality selection; key handling via useChannelKeyHandler
     StreamListScreen.tsx      — Language-filtered stream list DE/EN (A=direct play, X=channel page)
-    SettingsScreen.tsx        — streamBadgeMode, sidebarWidth, badgeGap, hlsCacheEnabled, fileLoggingEnabled
+    SettingsScreen.tsx        — language, streamBadgeMode, sidebarWidth, badgeGap, hlsCacheEnabled, fileLoggingEnabled
     AccountScreen.tsx         — User info, logout (with confirmation dialog)
+  i18n/
+    de.ts                     — German message catalog; source of truth for translation keys
+    en.ts                     — English message catalog typed against the German key set
+    useT.ts                   — Translation hook + static translator for non-React contexts
   components/
     VideoPlayer.tsx           — hls.js <video> wrapper, forwardRef (seek, seekTo, pause, play, stop, getCurrentTime); attachMedia before loadSource; play() in MANIFEST_PARSED
     PlaybackOverlay.tsx       — DOM overlay (seek bar, channel info, gamepad hints, auto-hide); playState: 'playing'|'paused'
@@ -164,7 +169,7 @@ src/renderer/src/
     playback.ts               — OVERLAY_HIDE_DELAY_MS, DOUBLE_TAP_MS, POSITION_REPORT_INTERVAL_MS
     input.ts                  — AXIS_THRESHOLD, REPEAT_INITIAL_MS, REPEAT_INTERVAL_MS
   context/
-    SettingsContext.tsx        — localStorage settings (streamBadgeMode, sidebarWidth, badgeGap, hlsCacheEnabled, fileLoggingEnabled), CSS custom properties sync
+    SettingsContext.tsx        — localStorage settings (language, streamBadgeMode, sidebarWidth, badgeGap, hlsCacheEnabled, fileLoggingEnabled), CSS custom properties sync
   hooks/
     usePlaybackSession.ts     — Shared hook: hlsPayload, playState, videoRef, quality panel state, startLive/startVod/stop; used by AppShell + ChannelScreen
     useChannelKeyHandler.ts   — Mode-based key handler for ChannelScreen; 5 modes: chapter/playback-quality/playback/hero/shelf
@@ -297,7 +302,7 @@ All binding objects are held in a ref — the listener never needs to be re-regi
 - `getTopGames()` makes 40 parallel `/streams?game_id=<id>&first=100` calls to estimate viewer counts
 
 ### Settings Persistence
-- UI settings (badge mode, sidebar width, badge gap, HLS cache toggle, file logging toggle) → `localStorage` under key `t4sd:settings` (no IPC, no flicker on startup); changes are mirrored to the main process via IPC (`app:set-hls-cache-enabled`, `app:set-file-logging-enabled`)
+- UI settings (language, badge mode, sidebar width, badge gap, HLS cache toggle, file logging toggle) → `localStorage` under key `t4sd:settings` (no IPC, no flicker on startup); changes are mirrored to the main process via IPC (`app:set-hls-cache-enabled`, `app:set-file-logging-enabled`)
 - VOD history + resume → SQLite `history.db` in `userData/`
 - Twitch tokens → Electron `safeStorage` (OS keystore), file: `userData/twitch-tokens.bin`