Add flight comparator web app with full scan pipeline

Full-stack flight price scanner built on fast-flights v3 (SOCS cookie bypass):

Backend (FastAPI + SQLite):
- REST API with rate limiting, Pydantic v2 validation, paginated responses
- Scan pipeline: resolves airports, queries every day in the window, saves
  individual flights + aggregate route stats to SQLite
- Background async scan processor with real-time progress tracking
- Airport search endpoint backed by OpenFlights dataset
- Daily scan window (all dates, not monthly samples)

Frontend (React 19 + TypeScript + Tailwind CSS v4):
- Dashboard with live scan status and recent scans
- Create scan form: country mode or specific airports (searchable dropdown)
- Scan detail page with expandable route rows showing individual flights
  (date, airline, departure, arrival, price) loaded on demand
- AirportSearch component with debounced live search and multi-select

Database:
- scans → routes → flights schema with FK cascade and auto-update triggers
- Migrations for schema evolution (relaxed country constraint)

Tests:
- 74 tests: unit + integration, isolated per-test SQLite DB
- Confirmed flight fixtures in tests/confirmed_flights.json (50 real flights,
  BDS→FMM Ryanair + BDS→DUS Eurowings, scraped Feb 2026)
- Integration tests parametrized from confirmed routes

Docker:
- Multi-stage builds, Compose orchestration, Nginx reverse proxy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flight-comparator/.env.example

@@ -0,0 +1,67 @@
+# Flight Radar Web App - Environment Configuration
+# Copy this file to .env and customize for your environment
+
+# ============================================================================
+# Backend Configuration
+# ============================================================================
+
+# Server Settings
+PORT=8000
+HOST=0.0.0.0
+
+# Database
+DATABASE_PATH=/app/data/cache.db
+
+# CORS Origins (comma-separated)
+# Development: http://localhost:5173,http://localhost:3000
+# Production: https://yourdomain.com
+ALLOWED_ORIGINS=http://localhost,http://localhost:80
+
+# ============================================================================
+# Frontend Configuration
+# ============================================================================
+
+# API Base URL (used during build)
+VITE_API_BASE_URL=http://localhost:8000
+
+# ============================================================================
+# Docker Configuration
+# ============================================================================
+
+# Backend Port (external)
+BACKEND_PORT=8000
+
+# Frontend Port (external)
+FRONTEND_PORT=80
+
+# ============================================================================
+# Optional: Production Settings
+# ============================================================================
+
+# Logging Level (DEBUG, INFO, WARNING, ERROR, CRITICAL)
+LOG_LEVEL=INFO
+
+# Rate Limiting (requests per minute)
+RATE_LIMIT_SCANS=10
+RATE_LIMIT_LOGS=30
+RATE_LIMIT_AIRPORTS=100
+RATE_LIMIT_DEFAULT=60
+
+# Cache Settings
+CACHE_THRESHOLD_HOURS=24
+
+# ============================================================================
+# Notes
+# ============================================================================
+#
+# Development:
+#   - Use default settings
+#   - CORS allows localhost origins
+#   - Verbose logging enabled
+#
+# Production:
+#   - Set proper ALLOWED_ORIGINS
+#   - Use HTTPS if possible
+#   - Adjust rate limits as needed
+#   - Consider using environment-specific .env files
+#