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/MyMesh.cpp

@@ -690,6 +690,14 @@ void MyMesh::onCommandDataRecv(const ContactInfo &from, mesh::Packet *pkt, uint3
                                const char *text) {
   markConnectionActive(from); // in case this is from a server, and we have a connection
   queueMessage(from, TXT_TYPE_CLI_DATA, pkt, sender_timestamp, NULL, 0, text);
+  // If the on-device Admin screen sent this command (not the BLE/USB app's CLI
+  // terminal), also hand the reply straight to the UI -- queueMessage() above
+  // never displays TXT_TYPE_CLI_DATA on-device (see should_display), since that
+  // path also serves the app's terminal, which must keep working unaffected.
+  if (_ui && ui_pending_admin_reply && memcmp(&ui_pending_admin_reply, from.id.pub_key, 4) == 0) {
+    ui_pending_admin_reply = 0;
+    _ui->onAdminReply(from.id.pub_key, text);
+  }
 }
 
 void MyMesh::onSignedMessageRecv(const ContactInfo &from, mesh::Packet *pkt, uint32_t sender_timestamp,
@@ -1749,6 +1757,20 @@ static bool isAllZero(const uint8_t* buf, size_t n) {
   return true;
 }
 
+// Shared by the BLE/USB CMD_SET_CHANNEL handler below and the on-device
+// Channels add/edit/delete UI (ChannelsView) -- one place computing "was this
+// a delete" so the two callers can't drift on the cleanup step.
+bool MyMesh::setChannelLocal(uint8_t idx, const ChannelDetails& ch) {
+  if (!setChannel(idx, ch)) return false;
+  saveChannels();
+  // An all-zero secret is this codebase's "empty slot" sentinel (same check
+  // loadChannels()/saveChannels() use) -- drop anything that referenced it by
+  // index, the same way onContactRemoved() does for contacts.
+  if (_ui && isAllZero(ch.channel.secret, sizeof(ch.channel.secret)))
+    _ui->onChannelRemoved(idx);
+  return true;
+}
+
 void MyMesh::handleCmdFrame(size_t len) {
   if (cmd_frame[0] == CMD_DEVICE_QUERY && len >= 2) { // sent when app establishes connection
     app_target_ver = cmd_frame[1];                    // which version of protocol does app understand
@@ -2451,14 +2473,7 @@ void MyMesh::handleCmdFrame(size_t len) {
     ChannelDetails channel;
     StrHelper::strncpy(channel.name, (char *)&cmd_frame[2], 32);
     memcpy(channel.channel.secret, &cmd_frame[2 + 32], 32); // 256-bit key
-    if (setChannel(channel_idx, channel)) {
-      saveChannels();
-      // An all-zero secret is this codebase's "empty slot" sentinel (same
-      // check loadChannels()/saveChannels() use) -- the app just cleared this
-      // channel, so drop anything that referenced it by index, the same way
-      // onContactRemoved() does for contacts.
-      if (_ui && isAllZero(channel.channel.secret, sizeof(channel.channel.secret)))
-        _ui->onChannelRemoved(channel_idx);
+    if (setChannelLocal(channel_idx, channel)) {
       writeOKFrame();
     } else {
       writeErrFrame(ERR_CODE_NOT_FOUND); // bad channel_idx
@@ -2469,10 +2484,7 @@ void MyMesh::handleCmdFrame(size_t len) {
     StrHelper::strncpy(channel.name, (char *)&cmd_frame[2], 32);
     memset(channel.channel.secret, 0, sizeof(channel.channel.secret));
     memcpy(channel.channel.secret, &cmd_frame[2 + 32], 16); // 128-bit key
-    if (setChannel(channel_idx, channel)) {
-      saveChannels();
-      if (_ui && isAllZero(channel.channel.secret, sizeof(channel.channel.secret)))
-        _ui->onChannelRemoved(channel_idx);
+    if (setChannelLocal(channel_idx, channel)) {
       writeOKFrame();
     } else {
       writeErrFrame(ERR_CODE_NOT_FOUND); // bad channel_idx