shell: answer to the ipc target sessiond actually calls

Action::Overview shells out to `ipc call overview toggle`. The only handler
here was `search`, so that call reached nothing and the three-finger tap
did nothing, without an error anyone would see.

It has been invisible from the device because the shipped sessiond has no
`gesture` verb yet and refuses the op long before the executor runs, so
only the first half of the break was observable.

This makes the existing binding reach the surface it already names. What
the tap should raise is TASK-55 Q1 and is not decided here.

surfaces/quickshell/modules/ii/overview/Overview.qml

@@ -229,6 +229,32 @@ Scope {
         GlobalStates.overviewOpen = true;
     }
 
+    // sessiond calls `ipc call overview toggle` for `Action::Overview` — the
+    // three-finger-tap binding (`device_state.rs`) and anything else that
+    // reaches for the overview by name. Nothing answered to `overview`: the
+    // only target here was `search`, so the executor shelled out to a handler
+    // that did not exist and the tap did nothing, silently. Two things were
+    // hiding that — the shipped sessiond has no `gesture` verb at all and
+    // refuses the op before it gets this far, so the second half of the break
+    // could not be seen from the device.
+    //
+    // This makes the existing binding reach the surface it already names. It
+    // does not decide what the tap *should* raise; that is TASK-55's Q1, and
+    // the answer there may retarget this without changing it.
+    IpcHandler {
+        target: "overview"
+
+        function toggle(): void {
+            GlobalStates.overviewOpen = !GlobalStates.overviewOpen;
+        }
+        function open(): void {
+            GlobalStates.overviewOpen = true;
+        }
+        function close(): void {
+            GlobalStates.overviewOpen = false;
+        }
+    }
+
     IpcHandler {
         target: "search"