fix: persist sourceHandle/targetHandle so cluster edges survive reload

backend/app/db/database.py

@@ -32,6 +32,10 @@ async def init_db() -> None:
             await conn.exec_driver_sql("ALTER TABLE edges ADD COLUMN path_style TEXT")
         with suppress(Exception):
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN custom_icon TEXT")
+        with suppress(Exception):
+            await conn.exec_driver_sql("ALTER TABLE edges ADD COLUMN source_handle TEXT")
+        with suppress(Exception):
+            await conn.exec_driver_sql("ALTER TABLE edges ADD COLUMN target_handle TEXT")
 
 
 async def get_db() -> AsyncGenerator[AsyncSession, None]:

backend/app/db/models.py

@@ -58,6 +58,8 @@ class Edge(Base):
     speed: Mapped[str | None] = mapped_column(String)
     custom_color: Mapped[str | None] = mapped_column(String)
     path_style: Mapped[str | None] = mapped_column(String)
+    source_handle: Mapped[str | None] = mapped_column(String)
+    target_handle: Mapped[str | None] = mapped_column(String)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=_now)