Cinematic mode video recording with remote aperture/subject control

Requested by @momentsintimeusa in #206.

What the user wants

Record Cinematic mode video (shallow depth of field with rack focus, like the built-in Camera app) from the camera device, with the focus subject and simulated aperture controllable from the remote.

Platform facts

• iOS 26 opened Cinematic capture to third-party apps: AVCaptureSession with isCinematicVideoCaptureEnabled on AVCaptureMovieFileOutput, simulatedAperture on the device, and AVCaptureDevice.cinematicVideoCaptureSceneMonitoringStatuses for detected subjects. See WWDC25 session 319 "Capture cinematic video in your app".
• Supported on iPhone 13 and later; requires a Cinematic-capable format (1080p and 4K at 24/25/30 fps depending on device).
• The output carries depth/focus metadata, so focus can be edited afterwards in Photos.
• Tap-to-focus already exists in the app (action 21); in Cinematic mode a tap selects the tracked subject instead of setting a focus point.

Scope sketch

• Camera: a cinematic video mode in CaptureEngine/RecordingPipeline, gated on device + iOS 26, choosing a Cinematic-capable format.
• Wire: capability flag supports_cinematic_video, mode entry, and a SetSimulatedAperture command in FlatBufferSchemas.fbs (Unknown = 0 convention). Reuse the tap-to-focus point message for subject selection.
• Remote: mode picker entry plus an aperture control (f/1.4–f/16); tap on the preview selects the subject.
• Overlaps with the manual-controls work tracked in #206 (simulated aperture is one of those controls), so coordinate the design.

Open questions

• Does Cinematic capture require AVCaptureMovieFileOutput, or can the existing AVCaptureVideoDataOutput + AVAssetWriter pipeline carry it? If the former, recording would bypass RecordingPipeline's per-frame crop path.
• Monetization: part of "enable video" IAP or a Pro tier?

Start with the cinematic-mode scope in CaptureEngine and RecordingPipeline, then review FlatBufferSchemas.fbs and the existing tap-to-focus action 21. Resolve the AVCaptureMovieFileOutput versus AVAssetWriter question and coordinate with #206 before implementing. Done means the supported devices can record Cinematic video, expose aperture and subject selection remotely, and carry the required capability and mode messages.