fix(nodes): persist show_port_numbers across reloads

The Show Port Numbers toggle reset on every reload because the backend
never stored it: the column was missing from the Node model and the field
was stripped by NodeSave/NodeBase/NodeUpdate schemas, so canvas/save
silently dropped it.

Add the show_port_numbers column (idempotent migration), and the field to
the node schemas so it round-trips through save/load.

Add regression tests covering persistence and the default-false case.

Fixes #184

ha-relevant: yes

backend/app/db/database.py

@@ -91,6 +91,8 @@ async def init_db() -> None:
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN disk_gb REAL")
         with suppress(OperationalError):
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN show_hardware BOOLEAN NOT NULL DEFAULT 0")
+        with suppress(OperationalError):
+            await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN show_port_numbers BOOLEAN NOT NULL DEFAULT 0")
         with suppress(OperationalError):
             await conn.exec_driver_sql("ALTER TABLE nodes ADD COLUMN width REAL")
         with suppress(OperationalError):