Fix Windows thread edge background

[SunkenInTime]

Summary

Fixes a dark strip that could briefly appear along the right edge of the window when switching threads on Windows.

Electron can expose the window background for a moment while the page repaints. This change maps that surface to the app's existing --background color, so it stays aligned in both light and dark mode.

Screenshots

Before	After

Verification

• formatting, lint, and web typecheck
• tested thread switching in the Windows Electron app

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Note

Low Risk
Small theme/chrome styling changes with no auth, data, or API impact; limited to initial paint and theme-color sync behavior.

Overview
Fixes a brief dark strip on the right edge when switching threads in the Windows Electron app by keeping the exposed window background aligned with the app surface during repaints.

Dark mode base moves from #161616 to #0a0a0a in index.html (theme-color meta tags, boot script, and html.dark body) so early paint matches the design token used elsewhere.

Browser chrome sync in syncBrowserChromeTheme no longer samples main[data-slot='sidebar-inset'] / sidebar inner / body backgrounds. It sets html and body to var(--app-chrome-background) and derives the dynamic theme-color meta from that resolved color, matching the existing --app-chrome-background → --background wiring in CSS.

^{Reviewed by Cursor Bugbot for commit 1baad2b. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix dark mode background color for Windows thread edge

• Updates the dark mode background color from #161616 to #0a0a0a in index.html, affecting the CSS, boot script constant, and theme-color meta tags.
• Reworks syncBrowserChromeTheme in useTheme.ts to derive the browser chrome color from a new --app-chrome-background CSS variable on the root element, replacing the previous logic that read color from a sidebar or main surface element.

^{Macroscope summarized 1baad2b.}

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Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 7d8709c. Configure here.}

[macroscopeapp]

Approvability

Verdict: Approved

Simple UI fix that changes a dark background color value (#161616 → #0a0a0a) and simplifies theme color syncing logic by using a CSS variable instead of querying specific DOM elements. Changes are purely visual with no runtime behavior impact beyond styling.

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