FUSE: Implement SFTP remote connections

[efimsky]

Parent Issue

Part of #118 (FUSE-based Archive & Remote Browsing Feature)

Summary

Add SFTP browsing support using sshfs.

Dependencies

Requires #121 (MountManager integration with App)

Tasks

MountManager

• Implement mount_sftp(connection: str) -> Path | None

  • Parse connection string (user@host:/path)
  • Generate mount point using hash
  • Execute sshfs user@host:/path /mount/point
  • Track in active_mounts with mount_type='sftp'
  • Return mount point or None on failure

• Implement can_mount_sftp() -> bool

  • Return self.tools.sshfs

Menu Integration

• Add new Action enum values:

  CONNECT_SFTP = auto()

• Add "Connect" menu between File and Command in menu.py:

  Menu('Connect', [
      MenuItem('SFTP...', 'connect_sftp'),
      # ... more items in future phases
  ])

• Add 'connect_sftp': Action.CONNECT_SFTP to MENU_ACTION_MAP

App Methods

• Handle Action.CONNECT_SFTP in run loop
• Implement App._prompt_sftp_connect():
  • Show input dialog for connection string
  • Validate format (user@host:/path or user@host)
  • Call mount_manager.mount_sftp()
  • Navigate to mount point on success
  • Show error on failure

Input Dialog

• Create simple text input dialog for SFTP connection string
• Support format: user@hostname:/remote/path or user@hostname

Testing

• Test mount_sftp() calls sshfs with correct arguments
• Test mount_sftp() tracks mount with mount_type='sftp'
• Test can_mount_sftp() returns correct value based on tool availability
• Test SFTP menu item exists in Connect menu
• Test CONNECT_SFTP action triggers connection prompt

Files

• Modify: tnc/mount.py
• Modify: tnc/app.py
• Modify: tnc/menu.py
• Modify: tests/test_mount.py