feat: v0.4 — satellite imagery, KiwiSDR radio, LOCATE bar & security cleanup

New features:
- NASA GIBS (MODIS Terra) daily satellite imagery with 30-day time slider
- Esri World Imagery high-res satellite layer (sub-meter, zoom 18+)
- KiwiSDR SDR receivers on map with embedded radio tuner
- Sentinel-2 intel card — right-click for recent satellite photo popup
- LOCATE bar — search by coordinates or place name (Nominatim geocoding)
- SATELLITE style preset in bottom bar cycling
- v0.4 changelog modal on first launch

Fixes:
- Satellite imagery renders below data icons (imagery-ceiling anchor)
- Sentinel-2 opens full-res PNG directly (not STAC catalog JSON)
- Light/dark theme: UI stays dark, only map basemap changes

Security:
- Removed test files with hardcoded API keys from tracking
- Removed .git_backup directory from tracking
- Updated .gitignore to exclude test files, dev scripts, cache files

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

backend/main.py

@@ -92,7 +92,8 @@ async def live_data_slow(request: Request):
         "frontlines": d.get("frontlines"),
         "gdelt": d.get("gdelt", []),
         "airports": d.get("airports", []),
-        "satellites": d.get("satellites", [])
+        "satellites": d.get("satellites", []),
+        "kiwisdr": d.get("kiwisdr", [])
     }
     # ETag based on last_updated + item counts
     last_updated = d.get("last_updated", "")
@@ -187,6 +188,13 @@ def api_region_dossier(lat: float, lng: float):
     """Sync def so FastAPI runs it in a threadpool — prevents blocking the event loop."""
     return get_region_dossier(lat, lng)
 
+from services.sentinel_search import search_sentinel2_scene
+
+@app.get("/api/sentinel2/search")
+def api_sentinel2_search(lat: float, lng: float):
+    """Search for latest Sentinel-2 imagery at a point. Sync for threadpool execution."""
+    return search_sentinel2_scene(lat, lng)
+
 # ---------------------------------------------------------------------------
 # API Settings — key registry & management
 # ---------------------------------------------------------------------------