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>

examples/companion_radio/ui-new/UITask.h

@@ -460,7 +460,6 @@ public:
   // (some used to leave the flag set, relying on onShow() to reset it) and keeps
   // the "did we touch flash?" answer in one place. Returns whether it saved.
   bool savePrefsIfDirty(bool& dirty);
-  void applyFont();
   void applyRotation();
   void applyFullRefreshInterval();
   uint32_t autoOffMillis() const {