Multi-bridge Phase 1.6: Test-center extension for dual-bridge fixtures

[tashda]

Why

Manual testing of the bridge switcher (#1.3) needs two live bridges. Today's docker-compose.yml runs only one mosquitto + z2m-bridge + seeder stack, so end-to-end multi-bridge flows can't be exercised locally.

What

• Extend docker-compose.yml with a second stack:
  • mosquitto-2 (port 1884)
  • z2m-bridge-2 (WebSocket port 8081, auth token shellbee-integration-token-2)
  • seeder-2 (control plane on port 8766)
• Make the seeder accept env vars to differentiate fixtures (e.g. SEED_FIXTURE_SET=alt) so the second bridge has a visually distinct device list — different friendly names, different device types, different signal strengths.
• Document the dual setup in CLAUDE.md ("Mock Z2M bridge for testing" section) including the URLs, tokens, and control plane ports.

Files

• docker-compose.yml
• docker/seeder/ — fixture selection via env var.
• CLAUDE.md — dual-bridge testing docs.

Verification

• docker-compose up brings both bridges online without port clashes.
• App can save and switch between localhost:8080 and localhost:8081. Each shows distinct devices.
• Both control planes (http://localhost:8765/ and http://localhost:8766/) are accessible and drive their respective bridges only.

Phase

Phase 1 of multi-bridge support. Independent — can land before #1.3 to enable testing.

[tashda]

Implemented in a33624f (Add dual-bridge docker stack for multi-bridge testing).