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>

utils/dependencies.py

@@ -195,6 +195,20 @@ TOOL_DEPENDENCIES = {
             }
         }
     },
+    'acars': {
+        'name': 'Aircraft Messaging (ACARS)',
+        'tools': {
+            'acarsdec': {
+                'required': True,
+                'description': 'ACARS VHF decoder',
+                'install': {
+                    'apt': 'sudo apt install acarsdec',
+                    'brew': 'brew install acarsdec',
+                    'manual': 'https://github.com/TLeconte/acarsdec'
+                }
+            }
+        }
+    },
     'satellite': {
         'name': 'Satellite Tracking',
         'tools': {