feat: add location names to reservation slots and promote-to-project

- Each monitoring location slot can now have a named location (e.g. "North Gate")
- Location names and slot order are persisted and restored in the planner
- Location names display in the expanded reservation card view
- Added "Promote to Project" button that converts a reservation into a
  tracked project with monitoring locations and unit assignments pre-filled

Requires DB migration on prod:
  ALTER TABLE job_reservation_units ADD COLUMN location_name TEXT;
  ALTER TABLE job_reservation_units ADD COLUMN slot_index INTEGER;

backend/models.py

@@ -518,3 +518,7 @@ class JobReservationUnit(Base):
 
     # Power requirements for this deployment slot
     power_type = Column(String, nullable=True)  # "ac" | "solar" | None
+
+    # Location identity
+    location_name = Column(String, nullable=True)  # e.g. "North Gate", "Main Entrance"
+    slot_index = Column(Integer, nullable=True)     # Order within reservation (0-based)