Add IR remote control (LIRC) with a number-key content mapping

Adds a TCP client for lircd's classic protocol: play/pause/next/prev/
volume/mute map to the same intents every other front-end already
emits, and number keys 0-9 play an assigned album/audiobook from the
start or a podcast show's newest episode, resolved fresh on every
press. The mapping is configured in config.yml and editable from the
frontend: a small "Taste zuweisen" button on the play screen (or the
A+digit keyboard shortcut) opens a 10-key picker to assign whatever is
currently playing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/components/HelpOverlay.tsx

@@ -10,6 +10,7 @@ const KEYS: Array<[caps: string[], label: string]> = [
   [["?"], "Einzelne Titel suchen"],
   [["F1"], "Diese Hilfe"],
   [["TAB"], "Musik / Hörbücher / Podcasts"],
+  [["A", "0-9"], "Aktuellen Titel einer Fernbedienungs-Taste zuweisen"],
   [["← ↑ ↓ →"], "Auswahl bewegen"],
   [["ENTER"], "Auswahl abspielen"],
   [["ESC"], "Schließen / Suche löschen"],