feat: re-run and delete scan from detail page

Backend:
- DELETE /api/v1/scans/{id} — 204 on success, 404 if missing,
  409 if pending/running; CASCADE removes routes and flights

Frontend (api.ts):
- scanApi.delete(id)

Frontend (ScanDetails.tsx):
- Re-run button: derives window_months from stored dates, detects
  country vs airports mode via comma in scan.country, creates new
  scan and navigates to it; disabled while scan is active
- Delete button: inline two-step confirm (no modal), navigates to
  dashboard on success; disabled while scan is active

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

flight-comparator/api_server.py

@@ -1337,6 +1337,42 @@ async def get_scan_status(scan_id: int):
         )
 
 
+@router_v1.delete("/scans/{scan_id}", status_code=204)
+async def delete_scan(scan_id: int):
+    """
+    Delete a scan and all its associated routes and flights (CASCADE).
+    Returns 409 if the scan is currently running or pending.
+    """
+    try:
+        conn = get_connection()
+        cursor = conn.cursor()
+
+        cursor.execute("SELECT status FROM scans WHERE id = ?", (scan_id,))
+        row = cursor.fetchone()
+
+        if not row:
+            conn.close()
+            raise HTTPException(status_code=404, detail=f"Scan not found: {scan_id}")
+
+        if row[0] in ('pending', 'running'):
+            conn.close()
+            raise HTTPException(
+                status_code=409,
+                detail="Cannot delete a scan that is currently pending or running."
+            )
+
+        cursor.execute("DELETE FROM scans WHERE id = ?", (scan_id,))
+        conn.commit()
+        conn.close()
+
+        logging.info(f"Scan {scan_id} deleted")
+
+    except HTTPException:
+        raise
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"Failed to delete scan: {str(e)}")
+
+
 @router_v1.get("/scans/{scan_id}/routes", response_model=PaginatedResponse[Route])
 async def get_scan_routes(
     scan_id: int,