Click highlight styles, rendered at export

[nftechie]

Context

Highlight clicks (setup window → More options → Capture details) currently sets SCStreamConfiguration.showMouseClicks, so ScreenCaptureKit draws its own click indicator into screen.mov. It can't be styled, and it can't be turned off after recording.

Instead, record click events and draw them at export, like the camera bubble. That way the style can be chosen, and changed, after recording.

Where to look

• The current flag: highlightClicks in Sources/Snapcap/App/RecorderSettings.swift → AppModel.runStart() → RecordingSession.Configuration.showsClicks → ScreenCaptureOptions.showsClicks in Sources/SnapcapCore/Capture/ScreenCapture.swift.
• CaptureTarget.globalFrame and AppModel.bubbleDragged(to:): how a global AppKit point becomes a normalized 0…1, top-left-origin position.
• RecordingSession.recordCameraMove and CameraOverlay.moves: the precedent for timed events in project.json.
• Sources/SnapcapCore/Render/FrameComposer.swift and OverlayChrome.swift: drawing and caching.
• Sources/SnapcapCore/Render/OverlayCompositor.swift: composer time is compositionTime + timeOffset.
• Sources/Snapcap/Views/EditorView.swift (PlayerStage): the live preview.

Proposal

• While recording, observe .leftMouseDown and .rightMouseDown with NSEvent.addGlobalMonitorForEvents. Global mouse monitors don't need Accessibility permission. Convert each click to a normalized position inside globalFrame, and ignore clicks outside it. For window captures, positions are relative to the window's frame at the start of recording; handling a window that moves can come later.
• Store something like "clicks": { "style": "ring", "color": {…}, "size": 1, "events": [{ "time": 4.1, "x": 0.42, "y": 0.63, "button": "left" }] }, with lenient decoding and a fingerprint entry.
• Offer styles such as an expanding ring that fades, a spotlight that dims everything but a circle, and a dot. Animate over about 0.45 s with the same easing as camera moves.
• Draw clicks relative to the fitted screen rectangle in FrameComposer, not the whole canvas. They're the same today, but won't be once backgrounds or 1:1 and 9:16 exports land.
• When rendered clicks are on, set showsClicks = false so indicators aren't doubled.

Acceptance criteria

• Clicks are stored in project.json with recording time and normalized position, and older projects still open.
• At least two styles, plus color and size, can be changed in the editor after recording, and the export matches the preview.
• Clicks outside the captured area are ignored, and region captures place clicks correctly. Unit test the coordinate conversion.
• There are no doubled indicators.
• Tests cover decoding, plus an export test with a fixture that includes a click.