Add an AltGr key; full-mode letters flick to their AltGr symbol

The right alt in full mode is now AltGr: sticky like the other modifiers,
it types the keymap's third/fourth level (sk: AltGr+J = ') instead of an
Alt shortcut. In hold-keys mode it holds the physical right alt, since
KWin resets the modifier state after an ISO_Level3_Shift keysym.

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

README.md

@@ -9,8 +9,9 @@ iPad-style floating on-screen keyboard for Plasma Wayland. Qt 6, C++ core, QML U
 - 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
 - Slide sideways on space to move the cursor; long-press space = trackpad (lines too); slide from `.?123` onto a symbol and release
-- Compact (iPad) or full (iPad Pro) keyboard: number row, punctuation, tab, caps lock, ctrl/alt/super, dead keys
+- Compact (iPad) or full (iPad Pro) keyboard: number row, punctuation, tab, caps lock, ctrl/alt/super/alt gr, dead keys
 - Ctrl/Alt/Super stick like shift (tap, double-tap, hold) and turn keys into shortcuts; a tapped or held shift joins them (Shift+F5, Shift+Tab, Shift+arrows), auto-shift and caps lock don't
+- Alt Gr (right of space in full mode) types the keymap's AltGr symbols (sk: Alt Gr+J = '), sticky like the others
 - Optional PC key blocks: function row, navigation (ins/home/pg up, del/end/pg dn, arrows), numeric keypad; any mix, typing keys included (⚙)
 - Floating: drag the bottom bar, resize from the corner; geometry is remembered per screen
 - Follows Plasma's virtual keyboard setting (tray toggle): off never pops up on focus, the default only after touch or a pen; "Always Show" and D-Bus `Show`/`Toggle` still show it
@@ -46,7 +47,7 @@ Dev hooks: `SLOPOSK_AUTOTYPE=text` commits on focus; `SLOPOSK_SCREENSHOT=file.pn
 
 Letters come from the system keymap (what KWin sends to every client): its Q/A/Z rows become the three letter rows. Letters elsewhere, e.g. Slovak ľščťž on the number row, become long-press alternates. The globe key switches the system layout over `org.kde.keyboard`, so the physical keyboard follows.
 
-In full mode every typing key comes from the keymap (number row, `[ ] \ ; ' , . /` or the layout's equivalents), with the shifted symbol shown above. Dead keys compose with the locale's XKB compose table.
+In full mode every typing key comes from the keymap (number row, `[ ] \ ; ' , . /` or the layout's equivalents), with the shifted symbol shown above (and flickable); letters, whose shift only capitalizes, show their AltGr symbol instead. Dead keys compose with the locale's XKB compose table.
 
 Everything else is `layouts/template.json`; `~/.local/share/sloposk/template.json` replaces it.
 
@@ -59,7 +60,7 @@ Everything else is `layouts/template.json`; `~/.local/share/sloposk/template.jso
 - `keysym`: sends the XKB keysym named by `keysym` (`Home`, `F5`, `Left`...) on press; `repeat` auto-repeats while held
 - `letters`: the keymap's letters in row `row` (0–2), with `flicks` handed out left to right
 - `keys`: every typing key in keymap row `row` (0 = number row … 3 = bottom)
-- `modifier`: `"modifier": "ctrl" | "alt" | "super"`; `capslock`
+- `modifier`: `"modifier": "ctrl" | "alt" | "super" | "altgr"`; `capslock`
 - Layer `full`: rows used instead of `rows` in full-keyboard mode
 - `stretch`: the key grows so its row is as wide as the layer's widest (letter counts vary by layout)
 - Top-level `alternates`: long-press choices per letter, after the keymap's own