feat: soundboard pads can load from a JSON5 file (DB fallback)

When the server (soundboard_sounds table) returns no pads, the client now
loads them from a JSON5 config file (loadGamedata accepts plain JSON and
JSON5). Useful when the DB / CMS isn't set up yet.

File-defined pads play locally for the clicker; DB-backed pads still go
through the server broadcast so everyone in the room hears them. Ships a
radio-style soundboard-sounds.json5.example template.

public/configuration/soundboard-sounds.json5.example

@@ -0,0 +1,20 @@
+{
+    // Soundboard pads loaded from a file — used as a FALLBACK when the server
+    // (soundboard_sounds DB table) returns no sounds. Copy this file to
+    // `soundboard-sounds.json5` (without .example) and add your sounds. JSON5:
+    // // comments and trailing commas are allowed.
+    //
+    // Fields:
+    //   id   - unique number (pad key)
+    //   name - label shown on the pad
+    //   url  - audio file URL (mp3/ogg/wav). Relative urls resolve against
+    //          `soundboard.url.prefix` (falls back to `asset.url`).
+    //
+    // NOTE: file-defined pads play LOCALLY for the person who clicks them. To
+    // broadcast a pad to everyone in the room, the sound must exist server-side
+    // in the soundboard_sounds table (same flow as custom badges). The file is
+    // the no-DB / offline option; the DB is the multiplayer one.
+    sounds: [
+        // { id: 1, name: 'Airhorn', url: 'https://your-host/airhorn.mp3' },
+    ],
+}