feat(docs): add the hero background glyph

[btravers]

Adds the project-specific line-art motif behind the home hero from the Claude Design docs mockup, in the site accent (self-contained data-URI in custom.css, hidden on mobile).

Note: this was meant to ride along with the 1.5.0 PR but got stranded when that merged first — hence this follow-up.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a home-page hero background “glyph” (an SVG line-art motif) to the VitePress docs theme via a CSS pseudo-element, intended to sit behind the hero content and be hidden on mobile.

Changes:

• Introduces a .VPHome::after pseudo-element with an inline SVG background image positioned top-right.
• Adds responsive behavior to hide the glyph on smaller screens.

[btravers]

Addressed all of the above in the latest push — reworked the glyph so it's robust and accent-driven:

• Encoding: the SVG is now base64-encoded, so no CSS parser/minifier can mangle the raw </>/spaces.
• Follows --accent: switched from background-image to a mask filled with background-color: var(--accent). (currentColor doesn't propagate into a background-image SVG, so a mask is the correct way to make the glyph track the accent token — and it also resolves the amqp #ff6d1f vs --accent mismatch.)
• Aspect ratio: replaced the fixed height with aspect-ratio: 500 / 300 so it scales proportionally with max-width (no letterboxing).
• Comment: reworded so it no longer implies the shared theme is the only thing setting .VPHome positioning.

Verified rendering locally (accent-colored glyph, incl. the text labels in unthrown's).