Invert dark mode tooltip colors

[shaunandrews]

Proposed Changes

• In dark mode, tooltips now use an inverted treatment: white background with black text, improving contrast against Studio's dark UI.
• The local @wordpress/ui patch exposes tooltip background and foreground CSS custom properties, so Studio can control tooltip colors without brittle generated selectors or wrapper-only workarounds.

Testing Instructions

• Run ENABLE_AGENTIC_UI=true npm start.
• Switch Studio to dark mode, then hover icon-only controls that render tooltips.
• Confirm tooltips use a white background with black text in dark mode.
• Switch to light mode and confirm the existing light-mode tooltip colors are unchanged.

[katinthehatsite]

The changes look good, I have one note regarding the testing instructions:

I had to first run:

rm -rf node_modules && npm install

to ensure that the patch was installed correctly. In case this helps other testers

[wpmobilebot]

📊 Performance Test Results

Comparing b16ff35 vs trunk

app-size

Metric	trunk	b16ff35	Diff	Change
App Size (Mac)	1315.63 MB	1315.63 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	b16ff35	Diff	Change
load	1102 ms	764 ms	338 ms	🟢 -30.7%

site-startup

Metric	trunk	b16ff35	Diff	Change
siteCreation	6510 ms	6527 ms	+17 ms	⚪ 0.0%
siteStartup	6552 ms	6557 ms	+5 ms	⚪ 0.0%

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Results are median values from multiple test runs.

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