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>

docs/solo_features/message_screen/message_screen.md

@@ -50,7 +50,7 @@ Posting to a **room server** requires a login handshake first, so the device can
 - **Log out** with **Hold Enter** on a room you're currently logged into → **Logout** (only offered once logged in). Forgets the saved password on the device, so the next time you open that room it prompts for one again instead of silently reusing the old one.
 - Passwords set from the **phone app** are saved on the device too, so it can post to that room standalone after a reboot.
 
-> The on-screen keyboard's default (Latin) page is ASCII only. Typing accented or non-Latin characters — Polish/Czech/German/French diacritics, Cyrillic, or Greek — needs Settings › Keyboard › Alphabet set to the matching alphabet first; the keyboard's **#@/abc** key then cycles Latin → that alphabet → Symbols → Latin. A password containing characters outside whatever's currently enabled can still be set from the phone app — the device stores and replays it byte-for-byte.
+> The on-screen keyboard's default (Latin) page is ASCII only. Typing accented or non-Latin characters — Polish, Czech, Slovak, German, French, Spanish, Portuguese or Nordic diacritics, Cyrillic, or Greek — needs Settings › Keyboard › Alphabet set to the matching language first; the keyboard's **#@/abc** key then cycles Latin → that alphabet → Symbols → Latin. A password containing characters outside whatever's currently enabled can still be set from the phone app — the device stores and replays it byte-for-byte.
 
 ---
 
@@ -129,6 +129,24 @@ In the **Rooms** list the context menu instead offers:
 | Notif: default / OFF / ON | Per-channel notification override — **LEFT/RIGHT** to cycle           |
 | Melody: global / M1 / M2  | Per-channel melody override — **LEFT/RIGHT** to cycle                 |
 | Fav: yes / no             | Add or remove this channel from favourites — **LEFT/RIGHT** to toggle |
+| Edit                      | Opens the Add/Edit form below, pre-filled with the channel's name    |
+| Delete                    | Removes the channel immediately (no confirm prompt)                   |
+
+---
+
+### Adding / editing a channel
+
+Joining a new community channel, or creating one to share with others, no longer needs the phone app. The **Channels** list ends with a **"+ Add channel"** row — press **Enter** on it to open the form, or use **Edit** from the context menu above to change an existing channel's name or secret.
+
+| Field  | Notes                                                                                        |
+| ------ | ---------------------------------------------------------------------------------------------- |
+| Name   | Up to 31 characters                                                                            |
+| Secret | **LEFT/RIGHT** toggles between two entry modes; **Enter** opens the keyboard for whichever is selected |
+
+- **Passphrase** (default) — type any text; the device hashes it down to the channel's 16-byte secret. Easiest to agree on verbally, the same idea as a room password — two people who type the same passphrase end up on the same channel.
+- **Hex key** — type the exact 32-hex-character secret (the format used by channel QR codes, see [QR Codes](../../qr_codes.md)), for joining a channel whose precise secret you were given rather than agreeing on a new passphrase.
+
+Select **[Save]** to commit. The secret can't be redisplayed once saved (only the derived key is kept) — editing it later means typing a new passphrase or hex key, the same as re-logging into a room with a new password.
 
 ---