feat: Enhance dashboard with filtering options and sync SLM status

- Added a new filtering system to the dashboard for device types and statuses.
- Implemented asynchronous SLM status synchronization to update the Emitter table.
- Updated the status snapshot endpoint to sync SLM status before generating the snapshot.
- Refactored the dashboard HTML to include filter controls and JavaScript for managing filter state.
- Improved the unit detail page to handle modem associations and cascade updates to paired devices.
- Removed redundant code related to syncing start time for measuring devices.

backend/services/slm_status_sync.py

@@ -0,0 +1,125 @@
+"""
+SLM Status Synchronization Service
+
+Syncs SLM device status from SLMM backend to Terra-View's Emitter table.
+This bridges SLMM's polling data with Terra-View's status snapshot system.
+
+SLMM tracks device reachability via background polling. This service
+fetches that data and creates/updates Emitter records so SLMs appear
+correctly in the dashboard status snapshot.
+"""
+
+import logging
+from datetime import datetime, timezone
+from typing import Dict, Any
+
+from backend.database import get_db_session
+from backend.models import Emitter
+from backend.services.slmm_client import get_slmm_client, SLMMClientError
+
+logger = logging.getLogger(__name__)
+
+
+async def sync_slm_status_to_emitters() -> Dict[str, Any]:
+    """
+    Fetch SLM status from SLMM and sync to Terra-View's Emitter table.
+
+    For each device in SLMM's polling status:
+    - If last_success exists, create/update Emitter with that timestamp
+    - If not reachable, update Emitter with last known timestamp (or None)
+
+    Returns:
+        Dict with synced_count, error_count, errors list
+    """
+    client = get_slmm_client()
+    synced = 0
+    errors = []
+
+    try:
+        # Get polling status from SLMM
+        status_response = await client.get_polling_status()
+
+        # Handle nested response structure
+        data = status_response.get("data", status_response)
+        devices = data.get("devices", [])
+
+        if not devices:
+            logger.debug("No SLM devices in SLMM polling status")
+            return {"synced_count": 0, "error_count": 0, "errors": []}
+
+        db = get_db_session()
+        try:
+            for device in devices:
+                unit_id = device.get("unit_id")
+                if not unit_id:
+                    continue
+
+                try:
+                    # Get or create Emitter record
+                    emitter = db.query(Emitter).filter(Emitter.id == unit_id).first()
+
+                    # Determine last_seen from SLMM data
+                    last_success_str = device.get("last_success")
+                    is_reachable = device.get("is_reachable", False)
+
+                    if last_success_str:
+                        # Parse ISO format timestamp
+                        last_seen = datetime.fromisoformat(
+                            last_success_str.replace("Z", "+00:00")
+                        )
+                        # Convert to naive UTC for consistency with existing code
+                        if last_seen.tzinfo:
+                            last_seen = last_seen.astimezone(timezone.utc).replace(tzinfo=None)
+                    else:
+                        last_seen = None
+
+                    # Status will be recalculated by snapshot.py based on time thresholds
+                    # Just store a provisional status here
+                    status = "OK" if is_reachable else "Missing"
+
+                    # Store last error message if available
+                    last_error = device.get("last_error") or ""
+
+                    if emitter:
+                        # Update existing record
+                        emitter.last_seen = last_seen
+                        emitter.status = status
+                        emitter.unit_type = "slm"
+                        emitter.last_file = last_error
+                    else:
+                        # Create new record
+                        emitter = Emitter(
+                            id=unit_id,
+                            unit_type="slm",
+                            last_seen=last_seen,
+                            last_file=last_error,
+                            status=status
+                        )
+                        db.add(emitter)
+
+                    synced += 1
+
+                except Exception as e:
+                    errors.append(f"{unit_id}: {str(e)}")
+                    logger.error(f"Error syncing SLM {unit_id}: {e}")
+
+            db.commit()
+
+        finally:
+            db.close()
+
+        if synced > 0:
+            logger.info(f"Synced {synced} SLM device(s) to Emitter table")
+
+    except SLMMClientError as e:
+        logger.warning(f"Could not reach SLMM for status sync: {e}")
+        errors.append(f"SLMM unreachable: {str(e)}")
+    except Exception as e:
+        logger.error(f"Error in SLM status sync: {e}", exc_info=True)
+        errors.append(str(e))
+
+    return {
+        "synced_count": synced,
+        "error_count": len(errors),
+        "errors": errors
+    }