Fix React performance and accessibility issues from react-doctor

[sejas]

Related issues

• Related to STU-1307

Proposed Changes

Address last set of warnings from react-doctor static analysis, except big refactors:

• Use lazy state initializer in edit-site-details.tsx to avoid calling getEffectiveWpVersion() on every render
• Extract default [] prop value to module-level constant in create-site.tsx and create-site-form.tsx to prevent new array reference each render
• Replace array index keys with content-based keys in welcome-message-prompt.tsx for stable React reconciliation when showMore toggles
• Always set role="button" with aria-disabled on sync site selector items instead of conditionally omitting the role

Testing Instructions

• Start the app with npm start
• Verify the Add Site modal works correctly (creates sites with expected domain names)
• Verify the AI chat welcome screen renders prompts and "show more" toggle works
• Verify the Sync modal site selector shows sites and allows selection
• Verify site settings can be edited (WordPress version selector)

React doctor:

• Run npx -y react-doctor
• Confirm that the following four warnings don't appear anymore:

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors? (Tests pass, no errors)

[wpmobilebot]

📊 Performance Test Results

Comparing e512b31 vs trunk

site-editor

Metric	trunk	e512b31	Diff	Change
load	1513.00 ms	1462.00 ms	-51.00 ms	🟢 -3.4%

site-startup

Metric	trunk	e512b31	Diff	Change
siteCreation	7091.00 ms	8133.00 ms	+1042.00 ms	🔴 14.7%
siteStartup	4952.00 ms	4944.00 ms	-8.00 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[epeicher]

Thanks @sejas for continue improving the codebase! I have tested the following:

Test	Result
Verify the Add Site modal works correctly (creates sites with expected domain names)	✅
Verify the AI chat welcome screen renders prompts and "show more" toggle works	✅
Verify the Sync modal site selector shows sites and allows selection	✅
Verify site settings can be edited (WordPress version selector)	✅

and I have not found any issues. LGTM!