feat(catalog): add MQTT home automation bridge service

[ctkm-aelf]

Summary

• Add a seeded MQTT catalog service backed by a local, node-routed HTTP bridge. The bridge exposes mapped device reads and explicit on/off actions while keeping broker credentials local.
• Register the hosted OpenAPI operations and an MQTT wordmark based on the IFTTT catalog icon style. Add the entry to the development preview catalog.
• Document MQTT setup, node credential storage, operation limits, and NyxID service types.

Test Plan

• Existing full suites pass (cargo test, npm run test across the repository). These were not run in full.
• New bridge and catalog tests added for the new functionality.
• Manually tested with a live MQTT broker and credential node. This remains to be done.

Focused checks passed:

• npm test in integrations/home-automation (10 tests)
• npm test -- src/components/dashboard/add-key-dialog.test.tsx in frontend (52 tests)
• npx tsc -b --pretty false in frontend
• cargo check -p nyxid --bin nyxid-server and cargo fmt --all -- --check in backend
• git diff --check origin/main...HEAD

Checklist

• Code follows the project's architecture rules.
• No hardcoded secrets or credentials.
• HTTP error responses do not expose bridge internals.
• Documentation updated.

[github-actions]

📊 Code coverage

Component	Lines	Threshold	Status	Δ vs base
Backend (nyxid)	87.07%	73%	✅	🔺 +0.01
Frontend (vitest)	72.21%	15%	✅	— 0.00

Gate: line coverage must stay at or above the threshold. Ratchet plan (W21): Backend → 55%, CLI → 50%, Frontend → 30% by quarter end.