Agentic UI: Remove theme toggle from sidebar user menu

[bcotrim]

Related issues

• Related to STU-1882

How AI was used in this PR

Implemented with Claude Code (Fable 5), manually validated.

Proposed Changes

• With the Appearance control now living in the Settings screen (PR 1 of this series), the sun/moon theme toggle in the sidebar user menu was redundant — two places controlling the same preference. This removes the sidebar toggle so appearance is managed in one predictable place: Settings.
• Also removes the now-unused sun/moon icons. No behavior change beyond the toggle's removal — the saved appearance preference still applies as before.

Testing Instructions

• Enable the Agentic UI and log in.
• Check the sidebar footer: the sun/moon appearance button should be gone; the user menu (Settings / Edit WordPress.com profile / Documentation / Report an issue / Log out) works as before.
• Log out: the login button and settings cog still render correctly.
• Change Appearance in Settings — the theme (and Gravatar dark variant) still updates.
• Verify sidebar footer spacing looks right in both light and dark mode.

Pre-merge Checklist

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

[wpmobilebot]

📊 Performance Test Results

Comparing b5dc009 vs trunk

app-size

Metric	trunk	b5dc009	Diff	Change
App Size (Mac)	1355.67 MB	1355.67 MB	0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	b5dc009	Diff	Change
load	1085 ms	759 ms	326 ms	🟢 -30.0%

site-startup

Metric	trunk	b5dc009	Diff	Change
siteCreation	6530 ms	6520 ms	10 ms	⚪ 0.0%
siteStartup	2392 ms	2392 ms	0 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

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

[nightnei]

I love such PRs xD

Confirm that everythign looks and works well