dotcli: Add shortcuts mechanism to dot kde save/apply/diff

Dispatches kglobalshortcutsrc identifiers through the kglobalaccel D-Bus
service instead of the schema-backed or freeform rc-file paths. Verified
manually against the live session (per the spec's testing decision, this
mechanism is excluded from the automated suite); switched to the
shortcutKeys/defaultShortcutKeys/setShortcutKeys D-Bus methods after the
spec's originally-named shortcut/defaultShortcut/setShortcut proved to
return stale data on the live system. Moves Lock Session off Meta+L to
Meta+X as the real-world validation, tracked in the manifest and recorded
in keybindings.md.

.github/keybindings.md

@@ -37,3 +37,4 @@ Comma-separated keys are pressed in sequence, not together.
 | `Space`, `e`                                           | neovim  | Toggle file explorer (netrw)                       |
 | `CapsLock`                                             | KDE     | Acts as `Esc` (`kxkbrc` `Options=caps:escape_shifted_capslock`) |
 | `Shift` + `CapsLock`                                   | KDE     | Toggles Caps Lock                                  |
+| `Meta` + `X`                                           | KDE     | Lock Session (moved off `Meta+L`, tracked via `dot kde`) |