ref(forms): Migrate project performance settings off JsonForm to scraps form

[priscilawebdev]

Summary

Migrates several sections of the Project Performance settings page from the legacy JsonForm/FormModel system to the new scraps form system (@sentry/scraps/form). Part of the ongoing JsonForm → scraps forms migration effort.

Migrated sections

• General (enable_images) → AutoSaveForm + Switch
• Threshold Settings (metric select + threshold input, plus the "Reset All" footer button) → two AutoSaveForm fields
• ### INTERNAL ONLY ### admin regression toggles (superuser-only: transaction/function duration regression) → AutoSaveForm + Switch

All behavior preserved: saveOnBlur semantics (auto-save on blur/change), analytics tracking, query-cache updates on success, disabled when the user lacks project:write, and the superuser 403 error message (now handled in the mutation onError). Mutations use fetchMutation<T> with typed mutationFn payloads — no call-site generics on useMutation/mutationOptions.

Intentionally left on JsonForm (documented for a follow-up)

• Sampling Priorities (dynamic-sampling) — uses a getData transform that reconstructs the full dynamicSamplingBiases array from all fields; not a clean per-field mapping. Untested/feature-gated, deferred to reduce risk.
• Performance Issues – Detector Threshold Settings — the large collapsible section with range sliders, per-panel admin toggles, and initiallyCollapsed behavior. This relies on JsonForm's forms/collapsible infrastructure and is heavily exercised by tests; left as-is.

This form is not registered for SettingsSearch (no data/forms entry, no generatedFieldRegistry entry), so no FormSearch wrapper or registry regeneration was needed.

Testing

• pnpm run typecheck (whole project) — pass
• pnpm run lint:js on the file — pass
• pnpm test-ci projectPerformance.spec.tsx — 42/42 pass (spec unchanged)