docker-compose.yml is tracked in a repo meant for publishing, so it can't
hold a real API key. Renamed it to docker-compose.yml.example (placeholder
values, safe to commit) and gitignored the real docker-compose.yml --
deploying is now "cp the example, fill in real values, docker compose up",
no .env file needed.
config.load() now reads IMMICH_URL/IMMICH_API_KEY from the environment
and applies them on top of whatever's in config.json, so setting them in
the compose file's environment: block takes effect without ever touching
the web UI. Env vars always win over the UI-saved values when both are
present -- verified they survive a save() with different UI-entered
values still in place.
Moves the existing ESP-IDF captive_portal example into firmware/ to make
room for the new FastAPI server and project docs, ahead of building out the
full ESPresso Frame project (ESP32-C6 + Immich-backed e-ink photo frame).