Improve context menus, add folder delete, fix dev version string

[antoninbas]

Summary

• Context menus: Right-click behavior is now meaningful for all entry types:
  • Top-level folders (notes/, logs/): Open only
  • User-created folders: Open + Delete (recursive, with confirmation)
  • Note files: Open + Edit (opens directly in edit mode) + Delete
  • Log files: Open + Delete (no Edit)
• Folder delete: New end-to-end deleteFolder capability (core/notes.ts → router → HTTP client → DELETE /api/notes/folder endpoint → frontend API helper)
• Dev version string: scripts/build.js now runs git describe at build time so dev builds show 0.11.0-dev.3+gabc1234 instead of the misleading plain 0.11.0

Bug fixes included

• Fixed Open action for folders in context menu (SolidJS signal was cleared before the path was read — now captured first)

Test plan

• Right-click notes/ or logs/ top-level folder → only "Open" appears, clicking it navigates in
• Right-click a user-created folder → "Open" and "Delete" appear; Delete removes folder and contents
• Right-click a note → "Open", "Edit", "Delete" all appear; Edit opens the note in edit mode
• Right-click a log → "Open" and "Delete" appear (no Edit)
• Build and check About modal shows version like 0.11.0-dev.N+gXXXXXXX

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