Fix the second dead settings button, and pin the class shut

A sweep for controls wired to targets the backend does not handle -- the shape
of the dictation bug -- found one more: "Start Orca" on the Accessibility page
called openApplication("orca") with no "orca" in the command map, so it set an
error and launched nothing. orca ships in hyprland-packages; it now runs.

That is the whole count. Every service-method call across 84 settings pages
resolves, every helper subcommand a service invokes is implemented, every
openGnomePanel handoff is allow-listed. Two dead buttons existed in the entire
settings app -- the dictation Download and this -- and both are fixed.

settings-buttons-contract pins the class: every openApplication id and
openGnomePanel panel a QML button passes must be present in SystemSettings'
dispatch maps, both of which return false silently on an unknown name.
Verified it catches the orca button when the fix is reverted.

And a dependency-contract exception the ffmpeg fix needed: ffmpeg is provided
by a swap (ffmpeg-free -> ffmpeg), never a list entry, because listing it is
the conflict that fix removed -- so panama-transcode's use of it is satisfied
without a package name to point at.

Claude-Session: https://claude.ai/code/session_01Epx9ZC1gwm81K3jm9x9CKh

config/dot/quickshell/services/SystemSettings.qml

@@ -644,7 +644,12 @@ Singleton {
             "rustdesk": ["rustdesk"],
             "kdeconnect": ["kdeconnect-app"],
             "mission-center": ["flatpak", "run", "io.missioncenter.MissionCenter"],
-            "bluebubbles": ["flatpak", "run", "app.bluebubbles.BlueBubbles"]
+            "bluebubbles": ["flatpak", "run", "app.bluebubbles.BlueBubbles"],
+            // The Accessibility page's "Start Orca" button. It was calling
+            // openApplication("orca") with no "orca" here, so it set an error
+            // and launched nothing -- a dead button. orca ships in
+            // hyprland-packages, so this just runs it.
+            "orca": ["orca"]
         };
         const command = commands[id];
         if (!command) {