Give each running game its own screen, capped at 10 concurrent

Previously every game shared one always-on Xvnc/fluxbox/websockify
desktop, so starting two games at once meant they fought over focus on
the same screen and the same ALSA device. Now:

- server.sh no longer starts a shared desktop at all - it just runs
  setup_server.py. There's no default display anymore.
- start_game() allocates a free display from GAME_DISPLAY_NUMS
  (:90-:99, one per MAX_CONCURRENT_GAMES=10 slot), spins up a fresh
  Xvnc+fluxbox+websockify for it, and launches the game with DISPLAY set
  to that display. All four processes are tracked together per game.
- stop_game() tears down all four; is_running() does the same lazily if
  the game exited on its own (crash/quit), so a slot doesn't stay stuck
  just because nobody clicked Stop.
- Starting past the 10-slot cap is refused with an error shown on that
  game's row instead of silently failing.
- Each running game's row gets its own "Open Screen" link (client-side
  JS, since the port is only known once the game is actually started)
  instead of one global noVNC link.
- run.sh publishes the whole 8090-8099 noVNC port range up front, since
  Docker can't add port mappings to an already-running container.

Verified end-to-end: two different games running concurrently get fully
independent Xvnc/fluxbox/websockify/game process sets and noVNC
endpoints; stopping one leaves the other untouched; the capacity guard
correctly refuses a start at the limit.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NiNnj78HGx1KWyCCo39HSz

scripts/server.sh

@@ -1,13 +1,6 @@
 #!/usr/bin/env bash
 set -x
 
-RFB_PORT=59${DISPLAY_NUM}
-NOVNC_PORT=80${DISPLAY_NUM}
 SETUP_PORT=70${DISPLAY_NUM}
 
-SETUP_PORT=${SETUP_PORT} NOVNC_PORT=${NOVNC_PORT} ${SCRIPTS_HOME}/setup_server.py &
-
-echo Display at ${DISPLAY} with ${SCREEN_W}x${SCREEN_H}x24
-Xvnc ${DISPLAY} -geometry ${SCREEN_W}x${SCREEN_H} -depth 24 +xinerama -securitytypes none >/var/log/xvfb.log &
-fluxbox &
-websockify -D --web=/usr/share/novnc/ --cert=/tmp/novnc.pem --key=/tmp/novnc.key ${NOVNC_PORT} localhost:${RFB_PORT}
+SETUP_PORT=${SETUP_PORT} exec ${SCRIPTS_HOME}/setup_server.py