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>

FEATURES.md

@@ -14,7 +14,7 @@ Hold Enter on the MESSAGE mode-select screen (DM / Channels / Rooms) opens a 1-i
 
 Implementation:
 - New `UITask::clearAllDMUnread()` — `memset` over `_dm_unread_table`
-- `QuickMsgScreen::clearAllChannelUnread()` already existed
+- `MessagesScreen::clearAllChannelUnread()` already existed
 - `UITask::clearRoomUnread()` already existed
 - Title is a `static const char*` table (PopupMenu stores the title pointer verbatim — locals would dangle)
 - Zero schema impact, all counters live in RAM
@@ -762,7 +762,7 @@ Unknown-secret packets no longer pollute the offline queue, UI history or trigge
 
 ### ✅ `addChannelMsg` guards against bogus index
 
-[`QuickMsgScreen.h:414-433`](examples/companion_radio/ui-new/QuickMsgScreen.h#L414-L433)
+[`MessagesScreen.h:414-433`](examples/companion_radio/ui-new/MessagesScreen.h#L414-L433)
 
 Defensive `if (ch_idx >= MAX_GROUP_CHANNELS) return;` at function entry — prevents ring-buffer pollution in case any future caller forgets the upstream guard. With C1 fixed this should never trigger, but the cost is zero.
 
@@ -787,7 +787,7 @@ Fixed: the save loop now skips unused slots (all-zero secret) instead of writing
 ```cpp
 if (msgcount == 0) {
     memset(_dm_unread_table, 0, sizeof(_dm_unread_table));
-    ((QuickMsgScreen*)quick_msg)->clearAllChannelUnread();
+    ((MessagesScreen*)messages_screen)->clearAllChannelUnread();
 }
 ```
 
@@ -795,7 +795,7 @@ When the companion app reads the last message from the offline queue, all on-dev
 
 ### ✅ Message buffers sized below the protocol maximum (clipped long messages)
 
-[`QuickMsgScreen.h`](examples/companion_radio/ui-new/QuickMsgScreen.h), [`KeyboardWidget.h`](examples/companion_radio/ui-new/KeyboardWidget.h)
+[`MessagesScreen.h`](examples/companion_radio/ui-new/MessagesScreen.h), [`KeyboardWidget.h`](examples/companion_radio/ui-new/KeyboardWidget.h)
 
 `ChHistEntry::text` was 140 B and `DmHistEntry::text` only 80 B, while the
 keyboard capped input at 139 B — all below MeshCore's `MAX_TEXT_LEN` (160 B).
@@ -870,13 +870,13 @@ Re-checked: `BOT_SCRATCH` is 200 and `MAX_TEXT_LEN` is 160, so an incoming messa
 
 ### ✅ `strncpy("?", buf, sizeof(buf))` replaced with `strcpy`
 
-[`QuickMsgScreen.h:785, 858`](examples/companion_radio/ui-new/QuickMsgScreen.h#L785)
+[`MessagesScreen.h:785, 858`](examples/companion_radio/ui-new/MessagesScreen.h#L785)
 
 Two fallback "?" sender names now use a plain `strcpy` so we don't memset 21 unused bytes for a one-character string.
 
 ### ❌ Title truncation in MSG_PICK reply mode — not an overflow
 
-[`QuickMsgScreen.h:1279-1287`](examples/companion_radio/ui-new/QuickMsgScreen.h#L1279)
+[`MessagesScreen.h:1279-1287`](examples/companion_radio/ui-new/MessagesScreen.h#L1279)
 
 Re-checked: `rlen` is clamped to 20 before building `"RE:" + nick`, so the title is ≤23 chars and fits `title[24]` with no overflow. A nick longer than 20 chars is shown truncated, but that's an intentional fit-to-header limit (the OLED header only fits ~21 chars anyway), not a bug.