Make the listen port configurable via PORT

app.py's dev server and gunicorn both hardcoded 5000, which is awkward
locally — macOS ControlCenter already holds that port, so the app can't
bind on the dev laptop without editing source.

Both now read PORT, defaulting to 5000 so EXPOSE, the compose
`${HOST_PORT}:5000` mapping and the deployed container are unchanged.
Read at run time rather than import time so a dev harness can assign a
free port.

Also tracks .claude/launch.json with autoPort set. It doesn't actually
launch on this machine — the preview sandbox can't read files under
~/Desktop — so CLAUDE.md notes that running from a shell with an
explicit PORT is the working local path.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

gunicorn.conf.py

@@ -1,8 +1,12 @@
 # Gunicorn configuration
+import os
+
 workers = 2       # 2 workers × 4 threads = 8 concurrent requests; fewer cold-cache workers
 threads = 4
 worker_class = "gthread"
-bind = "0.0.0.0:5000"
+# Defaults to 5000 to match EXPOSE, the `${HOST_PORT}:5000` mapping in
+# docker-compose.yml, and app.py's own dev-server default.
+bind = "0.0.0.0:" + os.environ.get("PORT", "5000")
 timeout = 30      # fail fast — app has its own 5s internal deadline
 keepalive = 5