The backend only stored bottom_handles, so top/left/right_handles were dropped
on canvas save and reset to defaults on reload — a left/right snappoint would
vanish after reload.
- models.py: add top_handles (default 1), left_handles (0), right_handles (0)
- database.py: ALTER TABLE migrations for the three columns
- schemas: add fields to NodeBase, NodeUpdate, and the canvas-save node schema
- tests: save+reload round-trip and default-fallback coverage
ha-relevant: no
Pouzor
6302c43e06