dotcli: add freeform mechanism to dot kde save/apply/diff

Read/write schema-less KDE settings (e.g. kxkbrc's Options= line)
directly via kreadconfig6/kwriteconfig6, with default defined as the
key being absent. diff only checks freeform entries already declared
in the manifest, never via undeclared broad scan.

Brings the machine's caps-lock/Escape swap under tracking as the
real-world validation case.

.config/dot/kde-manifest

@@ -0,0 +1 @@
+kxkbrc.Layout.Options=caps:escape_shifted_capslock