Add ACARS aircraft messaging feature with collapsible sidebar

- Add routes/acars.py with start/stop/stream endpoints for ACARS decoding
- Build acarsdec from source in Dockerfile (not available in Debian slim)
- Add acarsdec installation script to setup.sh for native installs
- Add ACARS to dependency checker in utils/dependencies.py
- Add collapsible ACARS sidebar next to map in aircraft tracking tab
- Add collapsible ACARS panel in ADS-B dashboard with same layout
- Include guidance about needing two SDRs for simultaneous ADS-B + ACARS
- Support regional frequency presets (N.America, Europe, Asia-Pacific)

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

routes/__init__.py

@@ -7,6 +7,7 @@ def register_blueprints(app):
     from .wifi import wifi_bp
     from .bluetooth import bluetooth_bp
     from .adsb import adsb_bp
+    from .acars import acars_bp
     from .satellite import satellite_bp
     from .gps import gps_bp
     from .settings import settings_bp
@@ -18,6 +19,7 @@ def register_blueprints(app):
     app.register_blueprint(wifi_bp)
     app.register_blueprint(bluetooth_bp)
     app.register_blueprint(adsb_bp)
+    app.register_blueprint(acars_bp)
     app.register_blueprint(satellite_bp)
     app.register_blueprint(gps_bp)
     app.register_blueprint(settings_bp)