Add MVP frontend scaffold with FastAPI + HTMX + TailwindCSS

- Created complete frontend structure with Jinja2 templates
- Implemented three main pages: Dashboard, Fleet Roster, and Unit Detail
- Added HTMX auto-refresh for real-time updates (10s interval)
- Integrated dark/light mode toggle with localStorage persistence
- Built responsive card-based UI with sidebar navigation
- Created API endpoints for status snapshot, roster, unit details, and photos
- Added mock data service for development (emit_status_snapshot)
- Implemented tabbed interface on unit detail page (Photos, Map, History)
- Integrated Leaflet maps for unit location visualization
- Configured static file serving and photo management
- Updated requirements.txt with Jinja2 and aiofiles
- Reorganized backend structure into routers and services
- Added comprehensive FRONTEND_README.md documentation

Frontend features:
- Auto-refreshing dashboard with fleet summary and alerts
- Sortable fleet roster table (prioritizes Missing > Pending > OK)
- Unit detail view with status, deployment info, and notes
- Photo gallery with thumbnail navigation
- Interactive maps showing unit coordinates
- Consistent styling with brand colors (orange, navy, burgundy)

Ready for integration with real Series3 emitter data.

backend/routers/units.py

@@ -0,0 +1,44 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.orm import Session
+from datetime import datetime
+from typing import Dict, Any
+
+from backend.database import get_db
+from backend.services.snapshot import emit_status_snapshot
+
+router = APIRouter(prefix="/api", tags=["units"])
+
+
+@router.get("/unit/{unit_id}")
+def get_unit_detail(unit_id: str, db: Session = Depends(get_db)):
+    """
+    Returns detailed data for a single unit.
+    """
+    snapshot = emit_status_snapshot()
+
+    if unit_id not in snapshot["units"]:
+        raise HTTPException(status_code=404, detail=f"Unit {unit_id} not found")
+
+    unit_data = snapshot["units"][unit_id]
+
+    # Mock coordinates for now (will be replaced with real data)
+    mock_coords = {
+        "BE1234": {"lat": 37.7749, "lon": -122.4194, "location": "San Francisco, CA"},
+        "BE5678": {"lat": 34.0522, "lon": -118.2437, "location": "Los Angeles, CA"},
+        "BE9012": {"lat": 40.7128, "lon": -74.0060, "location": "New York, NY"},
+        "BE3456": {"lat": 41.8781, "lon": -87.6298, "location": "Chicago, IL"},
+        "BE7890": {"lat": 29.7604, "lon": -95.3698, "location": "Houston, TX"},
+    }
+
+    coords = mock_coords.get(unit_id, {"lat": 39.8283, "lon": -98.5795, "location": "Unknown"})
+
+    return {
+        "id": unit_id,
+        "status": unit_data["status"],
+        "age": unit_data["age"],
+        "last_seen": unit_data["last"],
+        "last_file": unit_data.get("fname", ""),
+        "deployed": unit_data["deployed"],
+        "note": unit_data.get("note", ""),
+        "coordinates": coords
+    }