perf(camera): avoid duplicate capture encoding

[JustYannicc]

What changed

• Moved camera capture encoding into a small camera-specific helper module.
• Replaced the capture preview data URL with an object URL created from the same PNG blob used for disk save.
• Revoke the preview object URL when the preview clears and when the camera component unmounts.
• Added a focused regression test for the legacy duplicate encode baseline and the new single-encode path.

Why

The previous capture flow encoded the same canvas frame twice: once with toDataURL for preview and once with toBlob for saving. Data URLs also inflate memory. The new flow performs one toBlob encode, uses that blob for both preview and save, and keeps the saved file behavior unchanged.

Compatibility impact

• Camera preview UX is preserved: the latest capture thumbnail is still shown and fades/clears on the same timers.
• Saved PNG file behavior, save path, clipboard write, and last-capture open behavior are unchanged.
• Preview memory lifetime is improved because object URLs are explicitly revoked on clear and unmount.

How tested

• node --test scripts/test-camera-capture-single-encode.mjs
  • Legacy baseline mock confirms one capture would call toDataURL once and toBlob once.
  • Production helper path confirms toBlob is called once and toDataURL is not called.
  • Confirms object URL preview is shown and revoked on clear/dispose.
• ./node_modules/.bin/tsc --noEmit --jsx react-jsx --target ES2020 --module ESNext --moduleResolution bundler --strict --esModuleInterop --skipLibCheck --lib ES2020,DOM,DOM.Iterable src/renderer/types/electron.d.ts src/renderer/src/camera-capture.ts src/renderer/src/CameraExtension.tsx
• git diff --check origin/main...HEAD -- src/renderer/src/CameraExtension.tsx src/renderer/src/camera-capture.ts scripts/test-camera-capture-single-encode.mjs

Full renderer typecheck was also attempted with ./node_modules/.bin/tsc -p tsconfig.renderer.json --pretty false, but origin/main currently fails on unrelated renderer errors in files such as src/renderer/src/App.tsx, src/renderer/src/components/LiquidGlassSurface.tsx, launcher hooks, Raycast runtime files, settings, and quicklink icon utilities. No camera-file errors were reported by the scoped camera typecheck above.

No physical camera timing numbers were produced because this worker environment does not provide an Electron camera capture session/hardware harness. The regression test provides fresh encoder call-count validation for the performance issue.

Stack validation

• Branch codex/perf-camera-single-encode-pr was created from origin/main.
• git rev-list --left-right --count origin/main...HEAD reports 0 1.
• git log origin/main..HEAD contains only 70b0e5c perf(camera): avoid duplicate capture encoding.
• Diff is scoped to src/renderer/src/CameraExtension.tsx, src/renderer/src/camera-capture.ts, and scripts/test-camera-capture-single-encode.mjs.

[JustYannicc]

Superseded by consolidated upstream PR #534 (perf(mac): reduce native polling and async IO stalls), which carries this change together with the related macOS/native/audio/camera async IO performance fixes. Closing this source PR so review can continue on #534.