feat: sync indented Markdown tasks as subtasks

[kairan0]

Fixes #34

Summary

• Resolve the nearest preceding checkbox with less indentation when creating a native Markdown task.
• Send the linked parent's remote ID as parentId, inherit its project, and persist the server-confirmed placement locally.
• Stop creation when the parent is not linked or when the child explicitly names a different project.
• Handle spaces, tabs, and nested checkboxes inside blockquotes without changing root-task creation.

Safety boundary

This only affects the explicit Insert/create Dida task action for an unlinked Markdown checkbox. Editing the indentation of an already linked task does not reparent or unparent the remote task, because the same task can be referenced from multiple notes.

Testing

• npm test
• npm run build
• git diff --check

The repository-wide npx tsc --noEmit command still reports pre-existing Electron, Obsidian, and test typing errors; none point to the new production code.

[CYZice]

tomorrow I will review the PR and merge