v3: native bandcamp playback and a queue in the global player

The player now holds a queue instead of a single item, so albums play
through and single tracks share the same code path. Adds a "stream" item
kind for expiring, remotely-hosted sources: Bandcamp signs its mp3 URLs
for ~24h, so an item carries the page it came from and re-resolves itself
on error or on a stale restored session, falling back to the iframe embed
if that fails too.

Gated behind GERBEUR_BANDCAMP_PLAYER (default "embed"), injected into a
meta tag the same way as site-name/site-emoji.

Also: player header gains artwork and a subtitle, volume persists across
queue advances and reloads, and cross-origin streams get a plain seek bar
rather than a waveform that can never decode.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SbtjNsT5wvuABnfqhegZEJ

.env.example

@@ -14,6 +14,15 @@ GERBEUR_SITE_NAME=gerbeur
 # (server startup), so changing it only needs a restart — no rebuild.
 GERBEUR_SITE_EMOJI=🚚
 
+# How Bandcamp links are played.
+#   embed  (default) the bandcamp.com iframe — cannot autoplay
+#   native            resolve the page's mp3 streams and play them in gerbeur's
+#                     own player: autoplay, seeking, and albums as a queue.
+#                     Note this bypasses Bandcamp's player, so their play counts
+#                     and 3-play preview limit do not apply.
+# Applied at runtime; changing it needs a restart of both the API and Vite.
+GERBEUR_BANDCAMP_PLAYER=embed
+
 # Port the API server listens on (the container's internal port).
 GERBEUR_PORT=8000