Add SDL3-based controller input service

Integrate SDL3 controller support and wire it into the InputRouter.

- Add ControllerInputService (src/ControllerInputService.{h,cpp}) to discover, poll and translate SDL3 gamepad events into InputRouter actions, with axis repeat handling and debouncing.
- Update CMakeLists to find or fetch SDL3, add the new source files to the target, link the SDL3 target, and copy runtime DLLs on Windows.
- Add triggerAction(Action) to InputRouter and use it from existing keyboard handling to centralize action dispatch.
- Instantiate ControllerInputService in main so controllers feed the InputRouter.
- Update QML views (ShellWindow, HomeView, LibraryView, SettingsView) to use numeric action IDs and add small UI/status text and navigation tweaks for controller-driven flows.

These changes enable gamepad/controller input for Bigscreen via SDL3 and adapt UI code to handle the mapped actions.

Bigscreen/qml/ShellWindow.qml

@@ -70,7 +70,7 @@ ApplicationWindow {
                 window.handlePowerInput(action)
                 return
             }
-            if (action === InputRouter.Menu) {
+            if (action === 7) {
                 window.powerOverlayVisible = true
                 return
             }
@@ -120,16 +120,16 @@ ApplicationWindow {
 
     function handlePowerInput(action) {
         switch (action) {
-        case InputRouter.Up:
+        case 1:
             powerOverlay.moveFocus(-1)
             break
-        case InputRouter.Down:
+        case 2:
             powerOverlay.moveFocus(1)
             break
-        case InputRouter.Accept:
+        case 5:
             powerOverlay.activateFocused()
             break
-        case InputRouter.Back:
+        case 6:
             window.powerOverlayVisible = false
             break
         default:

Bigscreen/qml/views/HomeView.qml

@@ -39,15 +39,18 @@ ColumnLayout {
 
     function handleInput(action) {
         switch (action) {
-        case InputRouter.Left:
+        case 3:
             rail.moveFocus(-1)
             break
-        case InputRouter.Right:
+        case 4:
             rail.moveFocus(1)
             break
-        case InputRouter.Accept:
+        case 5:
             rail.activateFocused()
             break
+        case 6:
+            root.navigate("power")
+            break
         default:
             break
         }

Bigscreen/qml/views/LibraryView.qml

@@ -14,6 +14,7 @@ ColumnLayout {
     ]
 
     property int focusIndex: 0
+    property string statusText: "Mock entries for v0 — scanners and launchers come later."
 
     spacing: 20
 
@@ -25,7 +26,7 @@ ColumnLayout {
     }
 
     Text {
-        text: "Mock entries for v0 — scanners and launchers come later."
+        text: root.statusText
         font: Theme.metaFont
         color: Theme.textMuted
         Layout.leftMargin: 40
@@ -79,18 +80,19 @@ ColumnLayout {
 
     function handleInput(action) {
         switch (action) {
-        case InputRouter.Up:
+        case 1:
             focusIndex = Math.max(0, focusIndex - 1)
             list.currentIndex = focusIndex
             break
-        case InputRouter.Down:
+        case 2:
             focusIndex = Math.min(entries.length - 1, focusIndex + 1)
             list.currentIndex = focusIndex
             break
-        case InputRouter.Back:
+        case 6:
             root.goBack()
             break
-        case InputRouter.Accept:
+        case 5:
+            statusText = entries[focusIndex].title + " selected — launcher integration comes later."
             break
         default:
             break

Bigscreen/qml/views/SettingsView.qml

@@ -17,6 +17,8 @@ ColumnLayout {
 
     property int categoryIndex: 0
     property int itemIndex: 0
+    readonly property int settingCount: 3
+    property string statusText: "Choose a setting with Accept. Detailed controls come later."
 
     spacing: 20
 
@@ -73,7 +75,7 @@ ColumnLayout {
             }
 
             Repeater {
-                model: 3
+                model: root.settingCount
 
                 Rectangle {
                     Layout.fillWidth: true
@@ -93,26 +95,37 @@ ColumnLayout {
                     }
                 }
             }
+
+            Text {
+                text: root.statusText
+                font: Theme.metaFont
+                color: Theme.textMuted
+            }
         }
     }
 
     function handleInput(action) {
         switch (action) {
-        case InputRouter.Left:
+        case 3:
             categoryIndex = Math.max(0, categoryIndex - 1)
+            itemIndex = 0
             break
-        case InputRouter.Right:
+        case 4:
             categoryIndex = Math.min(categories.length - 1, categoryIndex + 1)
+            itemIndex = 0
             break
-        case InputRouter.Up:
+        case 1:
             itemIndex = Math.max(0, itemIndex - 1)
             break
-        case InputRouter.Down:
-            itemIndex = Math.min(2, itemIndex + 1)
+        case 2:
+            itemIndex = Math.min(settingCount - 1, itemIndex + 1)
             break
-        case InputRouter.Back:
+        case 6:
             root.goBack()
             break
+        case 5:
+            statusText = categories[categoryIndex] + " setting " + (itemIndex + 1) + " selected."
+            break
         default:
             break
         }