Initial build: fullhouse, live music bingo from a real Spotify playlist

Based on bingo-bango by f8al (MIT) — same core card-generation idea
("both facets": a square is either an exact song title or an artist,
and an artist square lights up on any of their tracks), reworked with
a real host/guest split, live multiplayer sessions, and cover-art
squares. f8al credited in the footer, README, and PROPOSAL.md.

Three ways to play: host a live session (server-side Spotify
connection, join code + QR, caller screen, auto-call from real
playback), join someone else's session (no login needed), or solo
(guest PKCE login or a pasted public playlist URL, one-off card).

Genuinely verified against a real Spotify account throughout, not
just built and assumed working — including two real bugs found and
fixed along the way (Spotify's playlist-tracks endpoint quietly
renamed to /items with a reshaped response; reading playlist tracks
needs real user auth even for public playlists, so the "no guest
login" public-playlist path routes through the host's connection
instead of a dead-end app-only token). Both Docker images built and
run together on a real network with the nginx proxy verified working
end-to-end, and auto-call confirmed detecting an actual track playing
live through Spotify Connect within one poll tick.

server/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "fullhouse-server",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "start": "node index.js",
+    "dev": "node --watch index.js"
+  },
+  "dependencies": {
+    "cookie-parser": "^1.4.7",
+    "dotenv": "^16.6.1",
+    "express": "^4.19.2"
+  }
+}