fix: make docs home page scrollbar span full page width

[mohamedmansour]

Summary

The docs home page (/docs) rendered its vertical scrollbar inset from the page's right edge instead of at the page edge.

The home <main class="main-content"> owns the page's vertical scrollbar (overflow-y: auto), but it also carried an inline style="max-width:1152px;margin:0 auto;". That centered the scroll container at 1152px, so its scrollbar floated inside that box rather than at the page edge.

Fix

• Remove the inline max-width/margin from .main-content on the home page so it fills its parent and owns the scrollbar at the page's right edge.
• Move the width constraint onto a new inner .home-container wrapper (max-width: 1152px; margin: 0 auto;) so the hero, feature grid, and footer stay centered.

Only the webui-press docs-site template assets changed (docs.css, index.html); no Rust, public API, protocol, or CLI behavior is affected. Non-home pages already use .main-content at full width and are untouched.

Verification

• Rebuilt the docs site and confirmed the generated dist/index.html / dist/docs.css reflect the change.
• In-browser at a wide viewport: .main-content now spans the full page width with its ~15px scrollbar flush at the right edge (right === pageWidth); .home-container stays 1152px centered. Mobile width and a non-home guide page render correctly with no console errors.

Closes #374