ADFA-5192 refactor(terminal): re-home the Debian terminal into TerminalActivity

[luisguzman-adfa]

Re-homes the Debian terminal out of the legacy MainActivity into its own thin
TerminalActivity, so MainActivity and the dead legacy tabbed UI can be removed
(ADFA-5192, Phase B — the deletion is Phase A / a separate PR).

Changes

• TerminalActivity (new): loads the native termux engine, hosts the terminal
  layout, implements TerminalController.Host (addToLog → LogRepository,
  vibrateDevice). All terminal behaviour stays in TerminalController, unchanged.
• terminal_activity.xml (new): the terminal_bottom_sheet subtree (drag handle,
  drawer, TerminalView, extra keys) lifted from main.xml, kept as a
  BottomSheetBehavior child of a CoordinatorLayout so TerminalController.bind()
  works without changes. Swipe-down finishes back to the caller, as the old
  terminal-only mode did.
• Manifest: TerminalActivity declared (not exported, singleTop, adjustResize
  • configChanges — the same window/IME setup MainActivity used for the terminal).
• The two callers now open TerminalActivity directly (no terminal-only extras):
  TerminalSessionService (keep-alive notification) and redesign/SettingsSubFragment
  (Settings → Terminal).

Notes

• TerminalController is untouched — it was already host-agnostic (finds its view
  IDs + the 2-callback Host).
• MainActivity keeps its terminal wiring for now; it is simply no longer launched
  by either caller. It is removed in Phase A.
• The terminal is a legitimately always-dark surface (like the QR black/white), so
  the layout's dark hex is carried over as-is; M3 token restyling is out of scope
  for a behaviour-preserving re-home.

Verification

Device build + manual: open the terminal from Settings → Terminal (Debian) and from
the keep-alive notification; type with the extra-keys bar over the keyboard;
swipe-down returns to the redesign. Sessions survive across open/close (app-scoped
session store).