ADFA-5192 refactor(ui): delete the legacy tabbed UI

[luisguzman-adfa]

Deletes the dead legacy tabbed UI (ADFA-5192, Phase A · Step 2). Nothing routed to it
since the redesign became the launcher; Phase B re-homed its last live use (the terminal)
into TerminalActivity, and Step 1 extracted the one shared symbol (SystemState).

Deleted

• MainActivity (+ its manifest ), MainPagerAdapter, and the four legacy
  fragments (Dashboard/Usage/Sync/Deploy).
• The carved controllers + Hosts: Install/Planner/ResetDelete/AdbShare (install),
  Backup (backup), Share/Receive/ArchCheck (sync).
• Legacy-only support views: ProgressButton (+ its styleable), ResourceGaugeView,
  MultiResourceGaugeView, ServerLogView, DashboardManager.
• Legacy layouts (main, fragment_dashboard/usage/sync/deploy, view_server_log) and the
  tab_* strings (base + all locales).

Kept

The install/backup/sync domain + service + repository layer (InstallService,
InstallProgressRepository, ModuleQueueRepository, InstallState, DownloadStateViewModel,
BackupEngine, SyncStateViewModel/SyncProgressRepository), ServerController/ServerState,
and the whole redesign package — all still used by the live UI.

Note

MainActivity hosted the cliReceiver for the terminal iiab CLI's backup/restore
broadcasts; those handlers were already cosmetic (the real trigger was long commented
out) and logged into the now-removed Usage console, so removing them is not a functional
change. The real fake-sysdata work (ACTION_PREPARE_ROOTFS) lives in
ServerController/EnvironmentControl and is unaffected.

Verification

No live-code or resource references to any deleted symbol remain (comments only). Needs
a device build: redesign launches normally, and the terminal opens from Settings and its
notification.

Tested on Device