fix(keyboard): count preview line breaks in codepoints, mark caps-lock

The text preview was the last part of the keyboard still working in bytes
rather than codepoints. cpl is how many characters physically fit on a
line, so dividing byte offsets by it counted every 2-byte Cyrillic/Greek/
accented character as two: lines held half the text they had room for, and
a break could land inside a codepoint. Both display drivers are
permanently single-font, so translateUTF8ToBlocks() passes UTF-8 straight
through -- the truncated sequence reached print() and drew as garbage on
both sides of the break. Line boundaries now walk the buffer with the same
kbUtf8*() helpers insertion/backspace/T9 already use, and the per-line
buffers are sized for a full line of 2-byte characters.

Caps-lock also gets an underline on the shift key: it sets caps too, so
the highlight alone made a one-shot Shift and a held lock indistinguishable
despite capitalising one letter vs. every following one.

Drops UITask::applyFont() -- setSingleFont() is a no-op on both drivers
since they were pinned to misc-fixed, so it did nothing, and use_lemon_font
has had no Settings row for a while. The pref itself stays: it's part of
the on-disk layout. Retires the matching stale rationale on scriptHint().

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

release-notes.md

@@ -19,7 +19,9 @@
 - **Triple-click could still toggle the buzzer while the screen was locked**, on boards that don't have a joystick (the single-user-button and analog-button variants) — the joystick variant already correctly suppressed it. Now consistent everywhere.
 - **Shift didn't capitalise ł, ń, ź, ż (or ĺ, ľ, ň, ž)** — a case-pairing rule for the wider Latin Extended-A block missed a parity flip around three unpaired codepoints, so e.g. typing "Łódź" with Shift held produced "łódź" instead. Fixed for the whole block.
 - **A long press on the physical button neither woke a sleeping display nor kept it awake**, and — while unlocked with the display off — could deliver its action to a screen you couldn't see, so the context menu was found already open at the next wake instead of the press simply waking the device. Long-press now goes through the same wake/keep-awake handling every other key already gets.
-- **Typing a character on CardKB right after cycling a T9 letter, then tapping that same T9 cell again quickly, could overwrite the character you'd just typed.** CardKB typing wasn't invalidating the pending T9 cycle the way every on-screen keypress already does.
+- **Typing on CardKB right after cycling a T9 letter, then tapping that same T9 cell again quickly, could overwrite an unrelated character.** None of CardKB's direct actions — typing, moving the cursor with the arrows, or opening the placeholder picker with Tab — were invalidating the pending T9 cycle the way every on-screen keypress already does, so the next tap "continued" the cycle against a moved cursor.
+- **The keyboard's text preview could split a Cyrillic, Greek or accented character in half at the end of a line**, drawing garbage on both sides of the break, and fitted only half as much text per line as it had room for. Line breaks in the preview were counted in bytes rather than characters — every other part of the keyboard already counted characters.
+- **Caps-lock and one-shot Shift looked identical on the keyboard's ⇧ key**, so there was no way to tell whether the next letter alone or every following letter would be capitalised. Caps-lock is now marked with an underline on the key.
 
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