feat(ipc): add settings dump to print full live config as JSON (#2817)

Adds `dms ipc call settings dump`, returning the complete live
configuration via SettingsData.getCurrentSettingsJson() — the same
serialization used by the read-only banner's copy button.

Useful when settings.json is a read-only symlink (NixOS/home-manager):
changes made in the Settings UI only exist in the running shell's
memory, and this makes them retrievable from the CLI instead of only
through the clipboard button in the Settings modal.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Port 1.5

(cherry picked from commit 846d07d86a)

quickshell/DMSShellIPC.qml

@@ -1003,6 +1003,10 @@ Item {
             return JSON.stringify(SettingsData?.[key]);
         }
 
+        function dump(): string {
+            return SettingsData.getCurrentSettingsJson();
+        }
+
         function set(key: string, value: string): string {
             if (!(key in SettingsData)) {
                 log.warn("Cannot set property, not found:", key);