Major security and code quality improvements

Security:
- Add input validation for all API endpoints (frequency, lat/lon, device, gain, ppm)
- Add HTML escaping utility to prevent XSS attacks
- Add path traversal protection for log file configuration
- Add proper HTTP status codes for error responses (400, 409, 503)

Performance:
- Reduce SSE keepalive overhead (30s interval instead of 1s)
- Add centralized SSE stream utility with optimized keepalive
- Add DataStore class for thread-safe data with automatic cleanup

New Features:
- Add data export endpoints (/export/aircraft, /export/wifi, /export/bluetooth)
- Support for both JSON and CSV export formats
- Add process cleanup on application exit (atexit handlers)
- Label Iridium module as demo mode with clear warnings

Code Quality:
- Create utils/validation.py for centralized input validation
- Create utils/sse.py for SSE stream utilities
- Create utils/cleanup.py for memory management
- Add safe_terminate() and register_process() for process management
- Improve error handling with proper logging throughout routes

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

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

routes/satellite.py

@@ -6,14 +6,22 @@ import json
 import urllib.request
 from datetime import datetime, timedelta
 from typing import Any
+from urllib.parse import urlparse
 
 from flask import Blueprint, jsonify, request, render_template, Response
 
 from data.satellites import TLE_SATELLITES
 from utils.logging import satellite_logger as logger
+from utils.validation import validate_latitude, validate_longitude, validate_hours, validate_elevation
 
 satellite_bp = Blueprint('satellite', __name__, url_prefix='/satellite')
 
+# Maximum response size for external requests (1MB)
+MAX_RESPONSE_SIZE = 1024 * 1024
+
+# Allowed hosts for TLE fetching
+ALLOWED_TLE_HOSTS = ['celestrak.org', 'celestrak.com', 'www.celestrak.org', 'www.celestrak.com']
+
 # Local TLE cache (can be updated via API)
 _tle_cache = dict(TLE_SATELLITES)
 
@@ -34,13 +42,18 @@ def predict_passes():
         return jsonify({
             'status': 'error',
             'message': 'skyfield library not installed. Run: pip install skyfield'
-        })
+        }), 503
 
-    data = request.json
-    lat = data.get('latitude', data.get('lat', 51.5074))
-    lon = data.get('longitude', data.get('lon', -0.1278))
-    hours = data.get('hours', 24)
-    min_el = data.get('minEl', 10)
+    data = request.json or {}
+
+    # Validate inputs
+    try:
+        lat = validate_latitude(data.get('latitude', data.get('lat', 51.5074)))
+        lon = validate_longitude(data.get('longitude', data.get('lon', -0.1278)))
+        hours = validate_hours(data.get('hours', 24))
+        min_el = validate_elevation(data.get('minEl', 10))
+    except ValueError as e:
+        return jsonify({'status': 'error', 'message': str(e)}), 400
 
     norad_to_name = {
         25544: 'ISS',
@@ -187,13 +200,19 @@ def get_satellite_position():
     try:
         from skyfield.api import load, wgs84, EarthSatellite
     except ImportError:
-        return jsonify({'status': 'error', 'message': 'skyfield not installed'})
+        return jsonify({'status': 'error', 'message': 'skyfield not installed'}), 503
+
+    data = request.json or {}
+
+    # Validate inputs
+    try:
+        lat = validate_latitude(data.get('latitude', data.get('lat', 51.5074)))
+        lon = validate_longitude(data.get('longitude', data.get('lon', -0.1278)))
+    except ValueError as e:
+        return jsonify({'status': 'error', 'message': str(e)}), 400
 
-    data = request.json
-    lat = data.get('latitude', data.get('lat', 51.5074))
-    lon = data.get('longitude', data.get('lon', -0.1278))
     sat_input = data.get('satellites', [])
-    include_track = data.get('includeTrack', True)
+    include_track = bool(data.get('includeTrack', True))
 
     norad_to_name = {
         25544: 'ISS',