fix(linux/wayland): collapse 3-step capture flow into a single portal dialog

Previously on Linux/Wayland, starting a fullscreen recording required three
separate picker interactions: an in-app source dropdown plus two xdg-desktop-portal
dialogs. The duplicate portal dialogs were caused by:

1. resolveBrowserCaptureSource() calling desktopCapturer.getSources() in the
   renderer, which itself triggers the portal on Wayland.
2. setDisplayMediaRequestHandler() in main also calling getSources(), which
   triggers another portal.
3. Returning a pre-enumerated source id to Chromium, which on Wayland is stale
   and forces Chromium to re-prompt via the portal during MediaStream creation.

Additionally, the editor window failed to appear after recording on some
Wayland sessions because 'ready-to-show' did not fire reliably.

Changes:
- LaunchWindow: skip the in-app source dropdown on Linux and start recording
  directly; the OS portal becomes the source picker.
- useScreenRecorder: introduce a 'screen:linux-portal' sentinel source. When
  set, route capture through navigator.mediaDevices.getDisplayMedia() so the
  portal handles selection in a single dialog. Skip resolveBrowserCaptureSource
  for the sentinel to avoid an extra getSources() call.
- electron/main: in setDisplayMediaRequestHandler, when the sentinel is set,
  skip desktopCapturer.getSources() entirely and return a synthetic source so
  Chromium opens the portal exactly once for the actual capture.
- electron/windows: in createEditorWindow, also call win.show() from
  did-finish-load as a fallback for Linux/Wayland where ready-to-show may
  not fire.

src/components/launch/LaunchWindow.tsx

@@ -1144,7 +1144,11 @@ export function LaunchWindow() {
 			<button
 				type="button"
 				className={`${styles.recBtn} ${styles.electronNoDrag}`}
-				onClick={hasSelectedSource ? toggleRecording : () => toggleDropdown("sources")}
+				onClick={
+					hasSelectedSource || platform === "linux"
+						? toggleRecording
+						: () => toggleDropdown("sources")
+				}
 				disabled={countdownActive}
 				title={t("recording.record")}
 			>

src/hooks/useScreenRecorder.ts

@@ -334,6 +334,14 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 			return source;
 		}
 
+		// Linux/Wayland portal sentinel: do NOT call getSources here, because
+		// on Wayland that triggers an additional xdg-desktop-portal dialog.
+		// The sentinel is handled later by routing through getDisplayMedia,
+		// which lets the portal pick the source in a single dialog.
+		if (source.id === "screen:linux-portal") {
+			return source;
+		}
+
 		try {
 			const liveSources = await window.electronAPI.getSources({
 				types: ["screen"],
@@ -827,7 +835,13 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 		setStarting(true);
 
 		try {
-			const selectedSource = await window.electronAPI.getSelectedSource();
+			const platform = await window.electronAPI.getPlatform();
+			const existingSource = await window.electronAPI.getSelectedSource();
+			const selectedSource =
+				existingSource ??
+				(platform === "linux"
+					? { id: "screen:linux-portal", name: "Linux Portal" }
+					: null);
 			if (!selectedSource) {
 				alert("Please select a source to record");
 				return;
@@ -841,8 +855,6 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 			recordingSessionTimestamp.current = Date.now();
 			resetRecordingClock(recordingSessionTimestamp.current);
 			await prepareWebcamRecorder();
-
-			const platform = await window.electronAPI.getPlatform();
 			const useNativeMacScreenCapture =
 				platform === "darwin" &&
 				(selectedSource.id?.startsWith("screen:") ||
@@ -1018,18 +1030,32 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 
 			if (wantsAudioCapture) {
 				let screenMediaStream: MediaStream;
+				const useLinuxPortal = selectedSource.id === "screen:linux-portal";
 
 				if (systemAudioEnabled) {
 					try {
-						screenMediaStream = await mediaDevices.getUserMedia({
-							audio: {
-								mandatory: {
-									chromeMediaSource: CHROME_MEDIA_SOURCE,
-									chromeMediaSourceId: browserCaptureSource.id,
-								},
-							},
-							video: browserScreenVideoConstraints,
-						});
+						screenMediaStream = useLinuxPortal
+							? await mediaDevices.getDisplayMedia({
+									audio: true,
+									video: {
+										displaySurface: "monitor",
+										width: { ideal: TARGET_WIDTH, max: TARGET_WIDTH },
+										height: { ideal: TARGET_HEIGHT, max: TARGET_HEIGHT },
+										frameRate: { ideal: TARGET_FRAME_RATE, max: TARGET_FRAME_RATE },
+										cursor: "never",
+									},
+									selfBrowserSurface: "exclude",
+									surfaceSwitching: "exclude",
+								})
+							: await mediaDevices.getUserMedia({
+									audio: {
+										mandatory: {
+											chromeMediaSource: CHROME_MEDIA_SOURCE,
+											chromeMediaSourceId: browserCaptureSource.id,
+										},
+									},
+									video: browserScreenVideoConstraints,
+								});
 					} catch (audioError) {
 						console.warn(
 							"System audio capture failed, falling back to video-only:",
@@ -1038,16 +1064,42 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 						alert(
 							"System audio is not available for this source. Recording will continue without system audio.",
 						);
-						screenMediaStream = await mediaDevices.getUserMedia({
-							audio: false,
-							video: browserScreenVideoConstraints,
-						});
+						screenMediaStream = useLinuxPortal
+							? await mediaDevices.getDisplayMedia({
+									audio: false,
+									video: {
+										displaySurface: "monitor",
+										width: { ideal: TARGET_WIDTH, max: TARGET_WIDTH },
+										height: { ideal: TARGET_HEIGHT, max: TARGET_HEIGHT },
+										frameRate: { ideal: TARGET_FRAME_RATE, max: TARGET_FRAME_RATE },
+										cursor: "never",
+									},
+									selfBrowserSurface: "exclude",
+									surfaceSwitching: "exclude",
+								})
+							: await mediaDevices.getUserMedia({
+									audio: false,
+									video: browserScreenVideoConstraints,
+								});
 					}
 				} else {
-					screenMediaStream = await mediaDevices.getUserMedia({
-						audio: false,
-						video: browserScreenVideoConstraints,
-					});
+					screenMediaStream = useLinuxPortal
+						? await mediaDevices.getDisplayMedia({
+								audio: false,
+								video: {
+									displaySurface: "monitor",
+									width: { ideal: TARGET_WIDTH, max: TARGET_WIDTH },
+									height: { ideal: TARGET_HEIGHT, max: TARGET_HEIGHT },
+									frameRate: { ideal: TARGET_FRAME_RATE, max: TARGET_FRAME_RATE },
+									cursor: "never",
+								},
+								selfBrowserSurface: "exclude",
+								surfaceSwitching: "exclude",
+							})
+						: await mediaDevices.getUserMedia({
+								audio: false,
+								video: browserScreenVideoConstraints,
+							});
 				}
 
 				screenStream.current = screenMediaStream;