Hold Keys mode: keys stay down while touched, like a hardware keyboard

- HardwareKeys presses a key's unshifted keysym on touch and releases it
  on lift, through fake input; held keys repeat and combine as on a
  physical keyboard (games, Shift+click)
- Shift/Ctrl/Alt/Super are plain held keys, caps lock is the system's,
  dead keys compose in the app
- No long-press, flick, trackpad or rollover in this mode; nothing is
  left held when the mode is turned off or touches are cancelled
- Settings switch; default stays the touch (virtual keyboard) mode

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

README.md

@@ -5,6 +5,7 @@ iPad-style floating on-screen keyboard for Plasma Wayland. Qt 6, C++ core, QML U
 - Flick a key down for its secondary symbol; long-press for accented alternates
 - iOS shift: tap = one letter, double-tap = caps lock, hold = shift while held
 - Works everywhere, not just in text fields: with none focused, keys reach the focused window like a hardware keyboard (shortcuts, terminals, the desktop); "Always Show" in ⚙ keeps it up
+- "Hold Keys" (⚙): keys stay down while touched, like a hardware keyboard (games, Shift+click, system key repeat); modifiers are plain keys, dead keys compose in the app; touch conveniences off
 - Letters follow the system keyboard layout; the globe key switches it
 - Auto-capitalization, double-space → ". " (both optional, ⚙ on the bottom bar), backspace repeat → word delete
 - Long-press space = trackpad; slide from `.?123` onto a symbol and release
@@ -61,7 +62,7 @@ Everything else is `layouts/template.json`; `~/.local/share/sloposk/template.jso
 
 ## Settings
 
-`~/.config/sloposk/sloposk.conf`, also editable from the ⚙ panel: `typing/autoCapitalize`, `typing/doubleSpacePeriod`, `layout/visibleSections` (`main` plus section ids), `layout/fullKeyboard`, `window/alwaysVisible`.
+`~/.config/sloposk/sloposk.conf`, also editable from the ⚙ panel: `typing/autoCapitalize`, `typing/doubleSpacePeriod`, `typing/holdKeys`, `layout/visibleSections` (`main` plus section ids), `layout/fullKeyboard`, `window/alwaysVisible`.
 
 ## Architecture