Fix double-space period, shift double-tap; settings; letters from system keymap

- Double-space replaced the space via a Backspace keysym, which clients
  apply after the commit: use delete_surrounding_text with the commit
- Tests use a shared FakeEngine that applies ops to a simulated field
- Double-tap shift locks at a sentence start; typing between taps doesn't
- Organization name set: config lives in ~/.config/sloposk/
- Settings (auto-capitalization, double-space period) with a ⚙ panel
- Letter rows come from the compositor's XKB keymap; other letters of the
  layout become long-press alternates; globe switches the system layout
  over org.kde.keyboard
- One JSON template for non-letter layers; stretch keys even out rows

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

README.md

@@ -4,7 +4,8 @@ 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
-- Auto-capitalization, double-space → ". ", backspace repeat → word delete
+- 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
 - Floating: drag the bottom bar, resize from the corner; geometry is remembered per screen
 
@@ -33,23 +34,23 @@ Dev hooks: `SLOPOSK_AUTOTYPE=text` commits on focus; `SLOPOSK_SCREENSHOT=file.pn
 
 ## Layouts
 
-JSON in `layouts/` (built in) or `~/.local/share/sloposk/layouts/` (overrides by `id`). The globe key cycles them; the system locale's comes first.
+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.
+
+Everything else is `layouts/template.json`; `~/.local/share/sloposk/template.json` replaces it.
 
 ```json
-{
-  "id": "sv-SE", "name": "Svenska", "locale": "sv_SE",
-  "base": "en-US",
-  "layers": [{"name": "letters", "rows": [[
-    "q",
-    {"label": "e", "flick": "3", "alternates": ["é", "è"]},
-    {"type": "backspace", "width": 1.5}
-  ]]}]
-}
+{"type": "letters", "row": 0, "flicks": ["1", "2", "3"]},
+{"type": "backspace", "width": 1.5, "stretch": true}
 ```
 
-- Key: a string, or an object with `type` (`char` `space` `backspace` `enter` `shift` `layer` `globe` `dismiss` `spacer`), `label`, `shifted`, `flick`, `alternates`, `width` (key units), `target` (for `layer`)
-- `base`: take layers this layout doesn't define (e.g. numbers/symbols) from another layout
-- Rows in a layer should add up to the same width; `tst_layoutloader` checks the built-ins
+- Key: a string, or an object with `type` (`char` `space` `backspace` `enter` `shift` `layer` `globe` `dismiss` `spacer` `letters`), `label`, `shifted`, `flick`, `alternates`, `width` (key units), `target` (for `layer`), `stretch`
+- `letters`: the keymap row `row` (0–2), with `flicks` handed out left to right
+- `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
+
+## Settings
+
+`~/.config/sloposk/sloposk.conf`, also editable from the ⚙ panel: `typing/autoCapitalize`, `typing/doubleSpacePeriod`.
 
 ## Architecture
 
@@ -57,10 +58,11 @@ JSON in `layouts/` (built in) or `~/.local/share/sloposk/layouts/` (overrides by
 qml/        view only
 input/      touch → PointerTracker gestures → KeyboardController rules
 engine/     key output → text ops (DirectEngine; prediction/swipe later)
-backend/    text ops → compositor (KWin input-method-v1)
-layout/     JSON → Layout → LayoutModel (geometry, hit testing)
+backend/    text ops → compositor (KWin input-method-v1); the compositor's keymap
+layout/     template JSON + keymap letters → Layout → LayoutModel (geometry, hit testing)
 window/     floating layer-shell placement, visibility, saved geometry
-app/        D-Bus control, dev hooks
+app/        D-Bus control and system layouts, dev hooks
+settings/   persisted user preferences
 ```
 
 `sloposk_core` (everything compositor-independent, plus the `Sloposk` QML module) is a static library shared by the app and the tests.