webapp: introduce Laravel app under webapp/ for scene overlays

Replaces the per-scene HTML directories (landing/, loading/, game/,
desktop/, goodbye/, music-box/, music/) with a single Laravel app
serving every overlay over HTTP. Supervisord runs `php artisan serve`
on 127.0.0.1:1118 and the OBS scene JSON now references HTTP routes
instead of file:// URLs.

Highlights:
 - public/css/hud.css consolidates the duplicated HUD chrome,
   scanlines/vignette/flicker, terminal styling, and pulse keyframes
   that were copy-pasted across all seven scenes.
 - Blade partials own hud-strip, crt-overlays, obs-ws-scripts,
   camera-frame, screen-frame; the seven scenes extend a shared
   overlay layout.
 - Artisan commands (`rig:setup`, `rig:telemetry`, `rig:loading`,
   `rig:playlist`, `rig:cmd`) replace the shell scripts that wrote
   per-rig JSON snapshots. TwitchHelix + HardwareSnapshot services
   handle the work the bash + Python helpers used to.
 - ObsWsClient + MusicCommandController kill the 250 ms cmd.js poll
   in the music daemon: POST /cmd/{skip|prev|pause|resume} opens a
   short-lived Pawl WS, authenticates, and broadcasts mpd:cmd.
 - AudioController streams files from the configured music dirs so
   CEF can load tracks under the HTTP origin (Chromium blocks
   HTTP-origin pages from loading file:// media).
 - DataController serves /data/playlist.js (with ETag mtime cache)
   and /cover.jpg (no-store) so the existing overlays' window.__PLAYLIST
   and cover.jpg cache-bust pattern keeps working.

scripts/obs-webapp.supervisord.conf is the supervisord unit; install
to /etc/supervisor.d/obs-webapp.conf.
scripts/rewrite-scene-urls.py is a one-shot tool that rewrites
basic/scenes/Default_Stream_HUD.json from file:// to HTTP URLs.
basic/scenes/Default_Stream_HUD.json.pre-webapp is the rollback
artifact (made with OBS closed; full pre-migration state).

The seven old scene directories, vendor/, and the bash scripts are
still on disk pending visual verification; the next commit will
prune them.

webapp/public/.htaccess

@@ -0,0 +1,25 @@
+<IfModule mod_rewrite.c>
+    <IfModule mod_negotiation.c>
+        Options -MultiViews -Indexes
+    </IfModule>
+
+    RewriteEngine On
+
+    # Handle Authorization Header
+    RewriteCond %{HTTP:Authorization} .
+    RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
+
+    # Handle X-XSRF-Token Header
+    RewriteCond %{HTTP:x-xsrf-token} .
+    RewriteRule .* - [E=HTTP_X_XSRF_TOKEN:%{HTTP:X-XSRF-Token}]
+
+    # Redirect Trailing Slashes If Not A Folder...
+    RewriteCond %{REQUEST_FILENAME} !-d
+    RewriteCond %{REQUEST_URI} (.+)/$
+    RewriteRule ^ %1 [L,R=301]
+
+    # Send Requests To Front Controller...
+    RewriteCond %{REQUEST_FILENAME} !-d
+    RewriteCond %{REQUEST_FILENAME} !-f
+    RewriteRule ^ index.php [L]
+</IfModule>