feat: Initial Hub implementation

Complete LetsBe Hub service for license management and telemetry:

- Client and Instance CRUD APIs
- License key generation and validation (lb_inst_ format)
- Hub API key generation (hk_ format) for telemetry auth
- Instance activation endpoint
- Telemetry collection with privacy-first redactor
- Key rotation and suspend/reactivate functionality
- Alembic migrations for PostgreSQL
- Docker Compose deployment ready
- Comprehensive test suite

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,13 @@
+# LetsBe Hub Configuration
+
+# Database
+DATABASE_URL=postgresql+asyncpg://hub:hub@db:5432/hub
+
+# Admin API Key (CHANGE IN PRODUCTION!)
+ADMIN_API_KEY=change-me-in-production
+
+# Debug mode
+DEBUG=false
+
+# Telemetry retention (days)
+TELEMETRY_RETENTION_DAYS=90