fix(ai-chat): emphasize pending Netclaw approvals

[Proxicon]

Closes #66

Summary

Pending Netclaw approvals could blend into the activity transcript, particularly in dark mode, and look like a stalled assistant. This PR makes an unanswered approval unmistakable while preserving the existing approval flow.

Implementation

• Adds a theme-aware warning callout and Approval required status in the activity heading and approval block.
• Keeps the original request text visible, supplies a polite status announcement, and adds data-testid="ai-assistant-approval".
• Makes allow keys prominent filled Primary actions; deny is an outlined Error action. Unknown future keys remain visible Primary actions.
• Adds wrapping desktop actions and full-width mobile actions with scoped CSS.
• Makes the deterministic fixture's access profile match its development token, preventing the session monitor from reloading the test page.
• Adds the dedicated AI Assistant Playwright suite to PR validation, run against the Release NewWeb artifact already built by the UX job.

Approval, API, and Netclaw semantics are unchanged: selected CallId and option key dispatch, busy disabling, and resolved-approval behavior remain in place.

Validation

• dotnet build src/HelpDesk.NewWeb/HelpDesk.NewWeb.csproj --configuration Release — passed.
• HELPDESK_AI_ASSISTANT_CONFIGURATION=Release npm run test:ux:ai-assistant — passed, 14/14 (light/dark desktop/mobile approval presentation and no-horizontal-overflow coverage included).
• tools/ci/check-public-disclosure.sh — passed.
• Pull request validation — passed, including the dedicated Release AI Assistant Playwright step.
• Managed PostgreSQL setup validation — passed.

Changed areas

• src/HelpDesk.NewWeb/Components/Shared/AiAssistantTurnActivity.razor
• src/HelpDesk.NewWeb/Components/Shared/AiAssistantTurnActivity.razor.css
• tests/ux/ai-assistant-chat.spec.ts
• tests/ux/ai-assistant-fixture-api.mjs
• tests/ux/auth.ts
• playwright.ai-assistant.config.ts
• .github/workflows/pull-request-validation.yml

Commits:

• 638c17294bb2deb54476cdbed13b824dd836e92c (fix(ai-chat): emphasize pending approvals (#66))
• 329cda10a3bbad302dfe641b9aa36938e0b78b2c (test(ai-chat): gate approval presentation coverage)

No migration, release, tag, deployment, or backend protocol change is included.