fix(computer-vision): align vision_camera segmentation overlay with preview

[msluszniak]

Description

In the computer-vision demo's vision_camera screen the semantic-segmentation overlay landed rotated and offset relative to the camera preview (FCN ResNet50 / any DeepLab variant). Two bugs in SegmentationTask.tsx:

• screenW/screenH were derived from an unconditional frame.height/frame.width swap, which is wrong outside portrait.
• The argmax.length === screenW * screenH branch was unreachable (runOnFrame is called with resizeToInput=false, so the mask is always at model output resolution) and we always fell into the sqrt(length) square fallback — which is fine for current square models but the subsequent <SkiaImage fit="cover"> over the whole canvas stretched it incorrectly onto the portrait canvas.

This PR:

• Derives screen-space W/H from frame.orientation ('left'/'right' swap, 'up'/'down' keep). The native side already rotates the mask into screen space via inverseRotateMat, so we just need the matching screen-space dims.
• Drops the unreachable screenW*screenH branch and uses sqrt(length) unconditionally with a comment noting that non-square model outputs would need dims plumbed from native.
• Draws the <SkiaImage> into the camera preview's cover-fit rect (Math.max scale + centering, same pattern as OCRTask) with fit="fill", so the mask aligns pixel-for-pixel with the preview.

Introduces a breaking change?

• Yes
• No

Type of change

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Documentation update (improves or adds clarity to existing documentation)
• Other (chores, tests, code style improvements etc.)

Tested on

• iOS
• Android

Testing instructions

1. Open the computer-vision demo → vision_camera screen.
2. Select Segment → FCN ResNet50 (or any DeepLab variant).
3. Aim the camera at a clear asymmetric subject (e.g. a TV).
4. The colored overlay should now line up with the actual subject in the preview, not rotated/displaced.

Screenshots

Related issues

Fixes #1158.

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation accordingly
• My changes generate no new warnings

Additional notes

iOS not retested with this patch — the orientation-aware swap is symmetric across platforms and the C++ rotation already handled iOS correctly, but a quick sanity check on a portrait iPhone before merge wouldn't hurt.