#220 Polish documentation menus and page navigation

Summary

• Standardize documentation dropdown sizing, spacing, icon styling, and hover colors using shared Tailwind color tokens.
• Align hover backgrounds across docs navigation, search, agent controls, and landing header links while preserving Copy Page button behavior.
• Restyle previous and next page links with the Copy Page inset-card treatment and shared hover border color.

Validation

• pnpm --filter web lint
• pnpm --filter web typecheck
• pnpm exec oxfmt --check on changed files

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Summary by cubic

Standardizes hover and menu styling across documentation and navigation components using new shared color tokens, and restyles previous/next page links to match the Copy Page inset-card treatment.

Key changes

• Adds subtle-hover, subtle-hover-border, and subtle-hover-foreground tokens for both light and dark themes.
• Deduplicates dropdown, context menu, and menubar item styling into shared constants.
• Simplifies the menubar to delegate styling, content, and keyboard handling to the shared dropdown-menu components.
• Switches docs sidebar, search, brand menu, and landing header hovers from muted to the new subtle-hover token.
• Rebuilds prev/next footer links as inset cards with an icon and shared hover border.

Summary by CodeRabbit

• Style
  • Updated hover states across navigation, buttons, and menus with subtler background, border, and text colors.
  • Refined dropdown and context-menu sizing, spacing, focus states, and icon styling.
  • Restyled documentation page navigation cards with a secondary background, directional icons, and clamped page titles.
  • Adjusted branding links and menu icons for a more consistent appearance.