UX: clarify naming between site-level and app-level Settings

[katinthehatsite]

Related issues

Fixes STU-1694

How AI was used in this PR

It was used to update the tests and do the implementation.

Proposed Changes

• Pull the changes from this branch
• Start Studio with npm start
• Confirm that the Settings tab is now changed to Site Settings
• Confirm that all the tests are passing

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[bcotrim]

Changes LGTM and work as described

[epeicher]

Thanks @katinthehatsite! I have tested it, and I can see the new Site Settings tab as expected. Also navigating to other tabs work as expected. I would say that once the E2E tests pass, this could be merged. LGTM!

[wpmobilebot]

📊 Performance Test Results

Comparing 550d664 vs trunk

app-size

Metric	trunk	550d664	Diff	Change
App Size (Mac)	2357.83 MB	2357.83 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	550d664	Diff	Change
load	1058 ms	1092 ms	+34 ms	⚪ 0.0%

site-startup

Metric	trunk	550d664	Diff	Change
siteCreation	6482 ms	6470 ms	12 ms	⚪ 0.0%
siteStartup	6991 ms	6998 ms	+7 ms	⚪ 0.0%

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Results are median values from multiple test runs.

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