feat(clock,keyboard): alarm repeat + non-Latin keyboard alphabets

Alarm repeat (Clock Tools):
- NodePrefs::alarm_repeat_mask (weekday bitmask, struct tm::tm_wday
  convention) — new Repeat row cycles Off/Daily/Weekdays/Weekends.
  computeAlarmNextFire() scans the next 7 days for a matching weekday when
  set; evaluateAlarm() only clears alarm_on (one-shot) when the mask is
  empty, otherwise re-arms. mask==0 is byte-for-byte the original one-shot
  behaviour, so existing users see no change.

On-screen keyboard alphabets (Settings > Keyboard > Alphabet):
- KeyboardWidget reworked from single-byte ASCII cells to UTF-8 codepoints
  (insertion, backspace and T9 in-place cycling all codepoint-aware now, so a
  multi-byte character is never split) — see kbApplyCapsUtf8/kbUtf8Len/
  kbUtf8CharAt/kbUtf8LastCharBytes.
- Cyrillic, Greek and an Extended Latin set (Polish/Czech/Slovak/German/
  French/Spanish/Nordic diacritics) join the keyboard's existing #@/abc page
  cycle (Latin -> alt alphabet -> Symbols -> Latin) — no new key needed.
  NodePrefs::keyboard_alt_alphabet picks which one, if any, is active.
- Lemon font is forced on transiently inside KeyboardWidget::render() (saved
  and restored every call) whenever the alt-alphabet page is showing or
  already-typed text has non-ASCII bytes, so composing is visible even if
  Font is set to Default.
- Each script's caps-shift rule is distinct and documented in
  kbApplyCapsUtf8: flat -0x20 for ASCII/Cyrillic/Greek (with the ё/ς
  exceptions), flat -0x20 for Latin-1 (à-þ), and an adjacent-pair -1 for
  Latin Extended-A (verified against every character actually used, not a
  blanket rule for that whole Unicode block).

NodePrefs schema: two tail-appended fields this session (alarm_repeat_mask,
keyboard_alt_alphabet), SCHEMA_SENTINEL 0xC0DE001B -> 0xC0DE001D,
sizeof(NodePrefs) 2496 -> 2504 (verified via a standalone host compile).

Docs: Clock Tools' Repeat row, Settings > Keyboard > Alphabet, and the
Rooms keyboard note (no longer ASCII-only once an alphabet is enabled).

Not build-verified — no PlatformIO toolchain available this session. Caps
mappings cross-checked against Python's Unicode case tables; UTF-8 literal
bytes verified at the byte level.

docs/solo_features/message_screen/message_screen.md

@@ -47,9 +47,10 @@ Posting to a **room server** requires a login handshake first, so the device can
 - **Passwords are remembered across reboots.** After a successful login the password is saved on the device, so picking that room again — even after a power cycle — logs back in silently and drops you straight into the chat.
 - **A wrong or changed password self-heals.** If a saved password stops working (e.g. the server's password was changed), the failed login forgets it, so the next **Enter** prompts you to type a new one.
 - **Re-login any time** with **Hold Enter** on the room → **Login…** (see the room context menu below) — useful to switch to a new password without waiting for a failure.
+- **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 is limited to ASCII (letters, digits and common symbols); accented characters such as `ą`/`ę` can't be typed on the device. A password containing them 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/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.
 
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@@ -105,11 +106,12 @@ A location is any `lat,lon` pair in the text — exactly what the `{loc}` placeh
 
 When **Pin to dial** is selected, a slot picker opens (Slot 1–6 showing current occupant name or "empty"). Choosing a slot that already holds another contact moves the new contact there.
 
-In the **Rooms** list the context menu instead offers a single item:
+In the **Rooms** list the context menu instead offers:
 
 | Item    | Action                                                                       |
 | ------- | ---------------------------------------------------------------------------- |
 | Login…  | Opens the password prompt to (re-)log in to this room (see Rooms — logging in) |
+| Logout  | Only shown once logged in. Forgets the saved password so the next open prompts for one again |
 
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