ARexx port for automation

[sidick]

ARexx port designed so the port never carries the passphrase (unlock is exclusively interactive). Command set: GETCODE, TIMELEFT, LIST (names only), STATUS, LOCK, UNLOCK (interactive prompt), SHOW/HIDE/QUIT. Optional per-vault "allow ARexx GETCODE" setting (default on). The security note must state plainly that any running program can drive the port while unlocked. From docs/ROADMAP.md v2 candidates + docs/SECURITY.md.

[sidick]

Notes from a GUI/style-guide review pass (see amiga-ui-style-guide skill's
shell-arexx-prefs.md), to fold in when this gets scoped/implemented:

• RC/RESULT conventions: the standard ARexx return-code band is
  0 = success, 5 = warning (e.g. aborted by user), 10 = error (e.g. wrong
  file type/bad otpauth URI), 20 = failure (e.g. couldn't reach the vault).
  Extended codes are fine as long as warnings stay below 10. Results should
  go in the RESULT variable, with VAR/STEM switches supported so
  callers can redirect into a named or stem variable (useful for LIST
  returning multiple account names: List.count, List.0, List.1, ...).
• QUIT should support FORCE/S to suppress any are-you-sure/confirm
  requester, matching the reserved meaning FORCE/S has across the standard
  15-command ARexx set (never repurpose it for something else).
• Port naming: standard convention is <BASENAME>.<slot#> in upper
  case (e.g. AMIAUTH.1), unique per instance, shown in the About window,
  overridable via a PORTNAME tooltype/arg. The existing private IPC port
  in src/amiga/guiport.h currently just uses the bare name "AmiAuth" for
  CLI-forwarding — worth deciding explicitly whether the ARexx port
  replaces/subsumes that private protocol or coexists alongside it under a
  distinct name, rather than ending up with two overlapping command
  channels.
• Command templates should parse via the standard ReadArgs()-style
  template method (verbose keywords, case-insensitive, COMMAND ? shows
  syntax help) for consistency with the CLI's own argument parsing.

None of this blocks the current command-set/security design already in the
issue description (passphrase-never-crosses-the-port is already correct)
— just conventions to apply once implementation starts.

[sidick]

Implemented in #104 (merged) — full ARexx port with GETCODE, TIMELEFT, LIST, STATUS, LOCK, UNLOCK (interactive-only passphrase prompt, same as the GUI's), SHOW/HIDE/QUIT, plus the arexxgetcode opt-out setting (default on, gates GETCODE/TIMELEFT). The passphrase never crosses the port — UNLOCK always opens the same interactive requester. See ARexx Port and Settings Reference for the full command/RC table and the security note.