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>

README.md

@@ -26,7 +26,7 @@ All firmware files are published on the [releases page](https://github.com/Marek
 
 ## Feature highlights
 
-- Extended language support with native Unicode rendering and input ([Lemon font](https://github.com/cmvnd/fonts)) alongside the original ASCII mode (Default font with transliteration)
+- Extended language support with native Unicode rendering and input ([Lemon font](https://github.com/cmvnd/fonts)) alongside the original ASCII mode (Default font with transliteration) — on-screen keyboard alphabets for Cyrillic, Greek, Polish, Czech, Slovak, German, French, Spanish, Portuguese and Nordic (Danish/Norwegian/Swedish), selectable in Settings › Keyboard › Alphabet
 
 - Enabled sensor screens with support for onboard sensors (temperature, humidity, pressure, luminosity, CO₂) and GPS data
 
@@ -41,7 +41,7 @@ All firmware files are published on the [releases page](https://github.com/Marek
   - **GPS trail** — background route recording with an auto-fit map (waypoints + live position), summary stats, auto-pause on stops, and [GPX export](#solo-tools)
   - **Metric or imperial** — one global Units setting drives every distance and speed across the UI
 
-- [Messages Screen](./docs/solo_features/message_screen/message_screen.md) — view and send messages, open message details, reply with quick messages or custom text, navigate to / save locations shared in a message, per-channel notification and melody overrides
+- [Messages Screen](./docs/solo_features/message_screen/message_screen.md) — view and send messages, open message details, reply with quick messages or custom text, navigate to / save locations shared in a message, per-channel notification and melody overrides, add/edit/delete channels on-device
 
 - [Favourites Dial](./docs/solo_features/favourites_dial/favourites_dial.md) — pin up to six contacts for quick access from the home screen
 
@@ -51,7 +51,7 @@ All firmware files are published on the [releases page](https://github.com/Marek
 
 - [Screen Lock](./docs/solo_features/screen_lock/screen_lock.md) — lock the device to prevent accidental keypresses, with a lock screen showing time and sensor data
 
-- [Tools Screen](./docs/solo_features/tools_screen/tools_screen.md) — GPS trail & waypoints, compass, nearby nodes (with ping & navigate), ringtone editor, auto-reply bot, auto-advert, live location sharing, locator, diagnostics, repeater
+- [Tools Screen](./docs/solo_features/tools_screen/tools_screen.md) — GPS trail & waypoints, compass, nearby nodes (with ping & navigate), ringtone editor, auto-reply bot, auto-advert, live location sharing, locator, diagnostics, repeater, remote admin
 
 - **Battery saving (radio)** — two optional, independent toggles under Settings › Radio:
   - **Pwr save** — hardware duty-cycle receive (SX126x `SetRxDutyCycle`): the radio cycles RX↔sleep on its own and wakes on a preamble, cutting average RX current with only a little added receive latency
@@ -99,7 +99,7 @@ Updating to a newer version usually does not require erasing flash unless the re
 | [Clock Screen](./docs/solo_features/clock_screen/clock_screen.md)          | Clock page, date, configurable data fields, alarm / timer / stopwatch  |
 | [Settings Screen](./docs/solo_features/settings_screen/settings_screen.md) | All settings sections with values and interactions                    |
 | [Screen Lock](./docs/solo_features/screen_lock/screen_lock.md)             | Lock/unlock sequence, lock screen, auto-lock                          |
-| [Tools Screen](./docs/solo_features/tools_screen/tools_screen.md)          | GPS trail & waypoints, compass, navigation, nearby nodes, ringtone editor, auto-reply bot, auto-advert, live location sharing, locator, diagnostics, repeater |
+| [Tools Screen](./docs/solo_features/tools_screen/tools_screen.md)          | GPS trail & waypoints, compass, navigation, nearby nodes, ringtone editor, auto-reply bot, auto-advert, live location sharing, locator, diagnostics, repeater, remote admin |
 | [Solo UI framework](./docs/design/solo_ui_framework.md)                    | **Developer guide** — the reusable building blocks (screens, lists, popups, mini-icons, geo/persistence helpers) and how to add a new feature |
 
 ### Upstream MeshCore