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>

python-backend/config.yml.example

@@ -66,6 +66,18 @@ general:
     # Built frontend to serve at /. Omit to expose only the JSON API.
     static_dir: ../web/dist
 
+  # IR remote control, over lircd's TCP socket (see ansible/roles/pi_lirc for how
+  # lircd itself is set up on the Pi). Omit the whole section to run without a remote.
+  # Play/pause/stop/previous/forward/rewind/volume/mute map to normal music control;
+  # number keys 0-9 play whatever the "remote:" section below assigns them.
+  lirc:
+    host: "musicmouse-pi.local"
+    port: 2222                 # this deployment's lircd listens on 2222, not its own
+                                # default of 8765 - see the ansible role
+    remote_name: "Hauppauge"   # other remotes registered with the same lircd (an LED
+                                # remote, say) are ignored
+    reconnect_interval: 5.0
+
   # Home Assistant integration. Omit the whole section to run without MQTT.
   # The backend exposes three lights, a player sensor, a volume slider, transport
   # buttons, device triggers for every button/touch area, and a tag scanner.
@@ -124,3 +136,20 @@ figures:
     id: "04b2c3d4e5"
     colors: ["#3355ff", "#66aaff", "#001133", "#ffffff"]
     kind: book
+
+# Number keys 0-9 on the IR remote, mapped to what they play. Omit the whole section,
+# or any digit within it, for "unassigned" - a fresh install boots with none of this
+# and that is not an error. Editable from the web front-end, which writes back here.
+#
+#   target_kind: album   -> always starts from the first track (music, audiobooks).
+#                            target is an album id, as shown at GET /api/library.
+#   target_kind: series  -> always plays the newest episode of a podcast show, resolved
+#                            fresh on every press - never a fixed episode. target is the
+#                            show's folder name under Kinderpodcasts, e.g. "Wissen macht Ah".
+remote:
+  "1":
+    target_kind: album
+    target: "3f9a0c12ab44"
+  "2":
+    target_kind: series
+    target: "Wissen macht Ah"