fix: show dot-prefixed tool folders in sidebar

[gzg1023]

Summary

• show common dot-prefixed AI and dev tool folders in the sidebar:
  • .agent
  • .claude
  • .codex
  • .cursor
  • .github
  • .vscode
• allow nested files and folders inside these directories through the Tauri filesystem scope
• keep noisy hidden entries such as .git, .DS_Store, .cache, and .env filtered
• add focused test coverage for visible and hidden dot-prefixed entries

Testing

• bun test
• bun run build
• cargo check
• git diff --check

Fixes #49