Full keyboard mode, Ctrl/Alt/Super, dead keys, shift levels

- Full (iPad Pro) mode: every typing key from the keymap, number row,
  tab, caps lock, ctrl/super/alt; shifted symbol shown above and flickable
- Dead keys compose with the locale's XKB compose table
- Ctrl/Alt/Super stick like shift and turn keys into shortcuts; a tapped
  or held shift joins shortcuts and non-text keys, auto-shift and caps
  lock don't
- Auto-capitalization and caps lock only capitalize letters; the user's
  shift picks the keymap's shifted level
- Mode switch in settings keeps key size by resizing the window

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/layout/KeyGeometry.h

@@ -29,3 +29,5 @@ inline QList<QRectF> computeKeyRects(const Layer &layer, QSizeF size, KeyboardMe
 qreal rowUnits(const Row &row);
 // Width of all blocks in key units, ignoring gaps.
 qreal totalUnits(const QList<Block> &blocks);
+// Rows of the tallest block.
+qsizetype totalRows(const QList<Block> &blocks);