test: drop screenshot suite (preview), keep gate-bypass infra

Per tho: don't add the screenshot test suite to this PR — it's not a
common path elsewhere yet, and the dedicated config / CI step / 12 PNGs
go with it.

Removed:
- desktop/playwright-screenshot.config.ts
- desktop/tests/e2e/screenshot-feature-flags.ts
- 12 screenshot PNGs under desktop/tests/e2e/screenshots/
- the Desktop screenshot e2e step from .github/workflows/ci.yml

Kept (genuine test infra, not a 'test addition' in tho's sense):
- bridge.ts seedPreviewFeatures option — preview features default-on in
  E2E so existing smoke specs (workflows.spec.ts etc.) can still reach
  preview-gated entry points
- tests/helpers/features.ts — single SoT for the seeding's preview ID
  list, derived from preview-features.json
- src/shared/features/resolveEnabled.test.mjs — unit coverage for code
  this PR added

Updated stale doc comment in bridge.ts that referenced the removed spec
by name.

Signed-off-by: npub1223z34hd7vtwc6qj4s7flsxkj644nlre2nthu7lrrmkumhu3xddsrx9r6w <52a228d6edf316ec6812ac3c9fc0d696ab59fc7954d77e7be31eedcddf91335b@sprout-oss.stage.blox.sqprod.co>

.github/workflows/ci.yml

@@ -170,8 +170,6 @@ jobs:
         run: just desktop-build
       - name: Desktop smoke e2e
         run: cd desktop && pnpm exec playwright test --project=smoke
-      - name: Desktop screenshot e2e
-        run: cd desktop && pnpm exec playwright test --config=playwright-screenshot.config.ts
       - name: Desktop Tauri check
         run: just desktop-tauri-check
         env: