refactor [NT-3230]: Use shared Preview Module in Web Preview Panel

[Felipe Mamud (fmamud)]

Summary

• Replace the Web Preview Panel's inline override-management code with the shared PreviewOverrideManager from @contentful/optimization-core/preview-support, aligning the Web panel with the React Native SDK and iOS JSC bridge that already consume the same module.
• Audience On/Off toggles now route through activateAudience/deactivateAudience, so audience-qualification snapshots and reset semantics match across platforms.
• Variant pickers route through setVariantOverride; the panel reset button routes through resetAll; per-audience Default clears via resetAudienceOverride.
• The web-only applyChangeOverrides (inline-variable → Variable changes) stays in the panel package — the shared module doesn't model the changes signal. It runs both as a state interceptor (on API refreshes) and synchronously from onOverridesChanged (on user clicks), so signals.changes and signals.selectedOptimizations always update in lockstep.
• localStorage persistence is preserved by subscribing to onOverridesChanged; overrides loaded from storage are hydrated into the manager on attach so first-render selections still reflect the prior session.

Test plan

Validation:

• pnpm typecheck — green across all packages
• pnpm lint — clean
• pnpm --filter @contentful/optimization-web-preview-panel build — succeeds, all bundle sizes under budget (umd 35.7k/38.5k, mjs 24.2k/26.5k, cjs 25.0k/27.5k gzip)
• pnpm --filter @contentful/optimization-core test:unit — PreviewOverrideManager coverage stays at 100%

End-to-end (against the web-sdk reference app + mock server):

• pnpm implementation:run -- web-sdk test:e2e (Playwright preview-panel.spec.ts)
  • Panel attaches and drawer toggles
  • Per-experience variant override updates rendered content + getFlag
  • Audience search/filter
• Audience-switch path (probed manually with a temporary spec):
  • On flips every experience under the audience to Variant 1
  • Off flips every experience under the audience to Baseline
  • Default clears the audience's overrides; natural qualification returns
• localStorage persistence — Baseline override survives a hard reload; Reset Profile clears __ctfl_opt_preview_overrides__ and __ctfl_opt_preview_defaults__
• Non-boolean inline-variable flags (json, number, plain-text) flip on Baseline/Variant 1 picks

[Charles Hudson (phobetron)]

Should we maybe migrate changes overrides to the Preview Support package, so we could similarly share that functionality with mobile (when we have someone who wants to make changes to mobile code 😅)?

[Felipe Mamud (fmamud)]

Should we maybe migrate changes overrides to the Preview Support package, so we could similarly share that functionality with mobile (when we have someone who wants to make changes to mobile code 😅)?

done in 578c91b.

Also, I've considered making those changes wiring into PreviewOverrideManager itself, but it pushed the Web Preview Panel UMD ~12 kB gzip over budget (34.9 became 46.4, budget was 38.5). So I've done only the helper one to be right.