Add welcome page with changelog and mode selection

- Replace simple splash screen with comprehensive welcome page
- Show version number and latest changelog entries
- Add 9-button mode selection grid for direct navigation
- User can now choose which mode to start with
- Responsive layout adapts to mobile screens
- Flow: Welcome → Disclaimer (if needed) → Selected mode

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

config.py

@@ -9,6 +9,40 @@ import sys
 # Application version
 VERSION = "2.9.0"
 
+# Changelog - latest release notes (shown on welcome screen)
+CHANGELOG = [
+    {
+        "version": "2.9.0",
+        "date": "January 2026",
+        "highlights": [
+            "New dropdown navigation menus for cleaner UI",
+            "TSCM baseline recording now captures device data",
+            "Device identity engine integration for threat detection",
+            "Welcome screen with mode selection",
+        ]
+    },
+    {
+        "version": "2.8.0",
+        "date": "December 2025",
+        "highlights": [
+            "Added TSCM counter-surveillance mode",
+            "WiFi/Bluetooth device correlation engine",
+            "Tracker detection (AirTag, Tile, SmartTag)",
+            "Risk scoring and threat classification",
+        ]
+    },
+    {
+        "version": "2.7.0",
+        "date": "November 2025",
+        "highlights": [
+            "Multi-SDR hardware support via SoapySDR",
+            "LimeSDR, HackRF, Airspy, SDRplay support",
+            "Improved aircraft database with photo lookup",
+            "GPS auto-detection and integration",
+        ]
+    },
+]
+
 
 def _get_env(key: str, default: str) -> str:
     """Get environment variable with default."""