refactor(docker): make image-based the default compose, build variant is .dev

Less confusion: docker-compose.yml is now the default (pulls pre-built images)
and the build-on-host variant is docker-compose.dev.yml. Updated all references
(CLAUDE.md, README, .env.example, build-push-images.mjs, compose header).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -122,10 +122,15 @@ TICKETMASTER_API_KEY=  # optional — free key from developer.ticketmaster.com
 
 ### 2. Start
 
+Build the images on the host (simplest — no registry needed):
+
 ```bash
-docker compose up -d
+docker compose -f docker-compose.dev.yml up -d
 ```
 
+The default `docker-compose.yml` instead **pulls pre-built images** from a registry (faster restarts;
+set `REGISTRY`/`TAG` in `.env`, `npm run push-images` from a dev machine, then `docker compose up -d`).
+
 Frontend on port 8080, backend on port 3700, scrobble service on port 3710. Route each through your reverse proxy. **Important:** the scrobble subdomain must *not* sit behind an SSO / forward-auth gateway — it authenticates itself via Navidrome (`ping.view`), and a gateway in front redirects the app's API calls to a login page.
 
 ### 3. First launch