v1.2.0

v1.2.0 — desktop, concurrent sessions, direct server-to-server transfer

Desktop
- New Linux, Windows and macOS builds alongside the Android app.
- CI packages tar.gz / zip / .app on every tagged release.
- Ubuntu PPA available at ppa:dhiva-labs/apps for `sudo apt install`.

Concurrent sessions
- Multiple servers open at once, one tab each.
- A background htop keeps running when you switch tabs; leaving the
  session screen no longer disconnects anything.
- Foreground service tracks the count and relabels ("2 sessions
  connected", then "srvB", then gone).

Move files between servers
- New "Copy to another server..." / "Move to another server..." in the
  file browser action sheet.
- On desktop, right-click the file, or drag it straight onto another
  session's tab.
- Two paths behind it: a relay through this device in RAM (no local
  disk touched), and a true direct A -> B via SSH agent forwarding
  where the bytes never even cross this machine. Direct is default
  when eligible; falls back to relay automatically if not.
- Move deletes the source only after four independent checks confirm
  the copy is intact on the destination.

Security
- Credentials on desktop go to the OS keyring: libsecret on Linux,
  DPAPI on Windows, login Keychain on macOS. No plaintext fallback
  anywhere - if the keyring is locked or missing, the save is refused
  and the user is told.
- App data on desktop lives in the platform's application-support
  directory, not the user's visible Documents folder.

Bug fixes
- Terminal buffer survives tab switching (Phase 12 regression fix).
- Retrying Save after a keyring failure no longer creates a duplicate
  host.
- Right-click on a file row now opens the action sheet on desktop
  (previously long-press only).