Implement meshinfo-network: full-stack React + FastAPI instance directory

[Copilot]

Replaces the minimal flat-file FastAPI prototype with a production-ready full-stack application serving as the central directory for MeshInfo instances.

Backend (backend/)

• FastAPI + SQLAlchemy ORM, SQLite by default with a clean Postgres path via DATABASE_URL
• Approval workflow: registrations start pending and are invisible publicly until manually approved — only status=approved + visibility=public rows appear in the API
• Token flow: POST /api/register generates a secrets.token_hex(32) key, stores SHA-256 hash, returns plaintext once; all subsequent writes (/heartbeat, /stats) require the token
• URL canonicalization: strips protocol/trailing slashes, lowercases host, preserves subdomains and path casing, enforced at registration and lookup
• Alembic migrations for instances, instance_stats_snapshots, instance_events

GET  /api/health
GET  /api/instances                       # approved + public only
GET  /api/instances/{id}
POST /api/register                        # returns token once
POST /api/instances/{id}/heartbeat        # token-authenticated
POST /api/instances/{id}/stats            # token-authenticated, coarse stats

Frontend (frontend/)

• React + TypeScript + Vite + Tailwind CSS v4, React Router — intentionally aligned with MeshAddicts/meshinfo conventions
• Dark mode with prefers-color-scheme detection and localStorage override
• Three pages: Home (what/how/privacy modes), Instances (searchable card list), Instance Detail
• Vite dev proxy routes /api/* → localhost:8000

Light	Dark

Supporting files

• docs/meshinfo-integration.md: concrete Phase 2 plan for adding opt-in reporting to MeshAddicts/meshinfo (config schema, token storage, re-registration, failure handling)
• README.md: full reference — dev setup, Docker, env vars, migrations, API, token flow, canonicalization rules, approval model
• docker-compose.yml / Dockerfile / Caddyfile: backend + frontend-build + Caddy reverse proxy

Removed

• api.py, requirements.txt, templates/ — old in-memory + JSON flat-file prototype

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