feat(ui): on-device channel management, remote admin tool, per-language keyboards

Messages:
- Add/edit/delete channels on-device (new ChannelsView, owned by the renamed
  MessagesScreen — was QuickMsgScreen, whose name no longer matched its scope).
  Channel secret entry supports a typed passphrase (SHA-256'd, same primitive
  the library already uses for the routing hash) or a raw 32-hex-char key.
- MyMesh::setChannelLocal() factors out the setChannel/saveChannels/
  onChannelRemoved sequence previously duplicated across the two
  CMD_SET_CHANNEL branches, shared now by the BLE and on-device paths.

Tools > Admin (new):
- Log into a repeater/room server's admin account and send CLI commands,
  the on-device equivalent of the app's repeater-admin feature.
- Commands are organised into category tabs (System/Radio/Routing/Actions)
  with common get/set fields (name, radio profile, tx power, repeat, advert
  intervals, ...) plus a free-text "Custom command..." fallback for anything
  else. A field row fetches the current value, opens it pre-filled for
  editing, and sends the change — falling back to a blank editor if the
  fetch fails or times out.
- The admin password persists and self-heals exactly like room logins in
  Messages: saved on a confirmed admin-level login, forgotten on a failed
  one, left alone if merely under-privileged.
- New MyMesh::sendAdminCommand()/AbstractUITask::onAdminReply() plumbing so
  a reply reaches the UI without touching the existing BLE/app CLI-terminal
  path (queueMessage's should_display gate is untouched).

Shared TabBar.h extracted from NearbyScreen/BotScreen's independently
duplicated tab-carousel rendering (now a third consumer via Admin) — also
fixes neighbouring tabs vanishing outright when they didn't fully fit;
they now truncate with an ellipsis instead.

Keyboard: the combined "Ext.Latin" alphabet split into 8 separate,
linguistically complete per-language keyboards (Polish, Czech, Slovak,
German, French, Spanish, Portuguese, Nordic), and fixed an OLED-only bug
where tall accented glyphs overlapped the keyboard's separator line
(SH1106's Lemon-font ascent constant was 2-3px short for them).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/companion_radio/AbstractUITask.h

@@ -51,6 +51,9 @@ public:
   // pub_key is the contact's key prefix (>=4 bytes valid); permissions is the
   // room/repeater ACL byte (only meaningful when success is true).
   virtual void onRoomLoginResult(const uint8_t* pub_key, bool success, uint8_t permissions) { (void)pub_key; (void)success; (void)permissions; }
+  // Text reply to an on-device-UI-triggered MyMesh::sendAdminCommand() arrived
+  // (see AdminScreen). pub_key is the contact's key prefix (>=4 bytes valid).
+  virtual void onAdminReply(const uint8_t* pub_key, const char* text) { (void)pub_key; (void)text; }
   // True only when a BLE central is actually bonded/connected. On a dual
   // (BLE+USB) interface hasConnection() is always true (USB counts), so use
   // this for BLE-specific UI like the pairing-PIN prompt.