feat: implement project status management with 'on_hold' state and associated UI updates

-feat: ability to hard delete projects, plus a soft delete with auto pruning.

backend/models.py

@@ -155,7 +155,7 @@ class Project(Base):
     name = Column(String, nullable=False, unique=True)  # Project/site name (e.g., "RKM Hall")
     description = Column(Text, nullable=True)
     project_type_id = Column(String, nullable=False)  # FK to ProjectType.id
-    status = Column(String, default="active")  # active, completed, archived
+    status = Column(String, default="active")  # active, on_hold, completed, archived, deleted
 
     # Project metadata
     client_name = Column(String, nullable=True, index=True)  # Client name (e.g., "PJ Dick")
@@ -166,6 +166,7 @@ class Project(Base):
 
     created_at = Column(DateTime, default=datetime.utcnow)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    deleted_at = Column(DateTime, nullable=True)  # Set when status='deleted'; hard delete scheduled after 60 days
 
 
 class MonitoringLocation(Base):