feat(deploy): consolidated dev stack with auto-provisioned Zitadel

Single docker-compose stack for local development (Postgres, Zitadel,
RabbitMQ, SeaweedFS + bucket init, Jaeger) plus an optional overlay to run
the .NET apps in Docker. up.ps1 orchestrates the full bootstrap: stack up,
stream-ticket keys, EF Core migrations and Zitadel provisioning.

- Zitadel is provisioned automatically (service-account PAT -> project +
  OIDC app with JWT access token); the generated ClientId is wired into
  Musify.Api user-secrets and .env. No manual console steps.
- ZITADEL_EXTERNAL_DOMAIN=host.docker.internal so token validation works
  both with local apps and full-docker.
- App Dockerfiles copy AppSettings*.json to lowercase so config loads on
  case-sensitive Linux; Worker image ships ffmpeg.
- Scripts split by responsibility (common/stream-keys/migrate/provision);
  apps overlay de-duped via YAML anchors.
- Remove the superseded standalone seaweedfs compose; point docs/development
  at the unified stack.

backend/.dockerignore

@@ -0,0 +1,10 @@
+**/bin/
+**/obj/
+**/.vs/
+**/.idea/
+.git/
+.github/
+.agents/
+.claude/
+**/DesignSettings.json
+*.user