Split inline CSS and SVG icons into separate files

[Copilot]

index.html from PR #1 embeds all styles in a <style> block and all icon paths as inline SVG strings in JS variables. This splits them into dedicated files.

Changes

• style.css — extracted from the <style> block; linked via <link rel="stylesheet" href="style.css">
• icon-dir.svg, icon-file.svg, icon-check.svg, icon-branch.svg, icon-chevron.svg — each icon extracted into its own SVG file containing a <symbol id="icon"> with the icon's path
• index.html — inline SVGs (both static HTML and JS ICON_* variables) replaced with <svg><use> references to the individual icon files:

// before
var ICON_DIR = '<svg width="16" height="16" viewBox="0 0 16 16"><path d="M1.75 1A1.75..."/></svg>';

// after
var ICON_DIR = '<svg width="16" height="16"><use href="icon-dir.svg#icon"></use></svg>';

CSS fill inheritance through <use> shadow DOM is preserved, so dark-mode theming continues to work without changes to style.css.

[casperdcl]

@copilot split icons.svg into separate files

[Copilot]

@copilot split icons.svg into separate files

Done in 2abb3bb. icons.svg has been replaced with five individual files — icon-dir.svg, icon-file.svg, icon-check.svg, icon-branch.svg, and icon-chevron.svg — each containing a <symbol id="icon"> with its path. All references in index.html updated accordingly.