feat: optimize canvas load and save using lazy loading and delta upserts

Implement custom templates and subscription tiers backend changes

fix: resolve foreign key constraint error when saving edges

fix: optimize SQLite write performance and re-enable WAL mode to resolve database locking

fix: refactor Edge.Condition to string for precise handle-based connection persistence

Extend TaskNode with visual and data fields to support images, drawing and custom text

feat(habits): support custom checked date in backend DTO, repository, and service

init