fix: separate dashboard and browser bookmarks; fix light theme contrast

[rudra-chothe]

Summary

Closes Issue #122

This PR fixes two issues:

1. Bookmarks data source separation

The BookmarksSection component was only reading from useBrowserBookmarks() (Chrome extension API), completely ignoring the bookmarks: BookmarkItem[] list managed by DashboardStateProvider. This meant app-saved bookmarks (persisted in localStorage) were never shown in the UI.

Changes:

• BookmarksSection now renders two distinct sections:
  • Bookmarks — dashboard-managed saved bookmarks from useDashboardState(), always visible, with inline add and delete support
  • Browser Bookmarks — Chrome API bookmarks (read-only, hidden entirely in dev mode)
• New SavedBookmarkItem component handles rendering of individual saved bookmarks with favicon, link, and delete button

2. Light theme contrast and card styling

All dashboard cards (glass-card) remained dark gray in light mode, and most interactive elements used hardcoded white/* opacity classes making them invisible on a light background.

Changes:

• .glass-card now uses a light/translucent background in light mode and dark/translucent in dark mode
• Stoic quote text (text-white) → text-foreground; author (text-white/50) → text-muted-foreground
• All bg-white/5, border-white/5, hover:bg-white/5, hover:bg-white/10 → foreground/* equivalents across DashboardHeader, TasksSection, TechNewsSection, BookmarksSection, TaskItem, SavedBookmarkItem
• Shortcut label text color made adaptive via var(--foreground)

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Type of Change

• Bug fix
• UI polish

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Screenshots / Screen Recording

Toggle between light and dark mode on the dashboard to observe:

• Cards change from dark-on-light to glass-dark-on-dark
• Quote text is clearly readable in both modes
• Bookmarks section shows saved bookmarks in both modes, browser bookmarks only in extension mode

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How to Test

1. Run npm run dev and open http://localhost:5173
2. Saved Bookmarks — Confirm 4 default bookmarks (Design reference, Typography, Color & contrast, Documentation) are visible
3. Add bookmark — Click + → enter a URL → press Save or Enter → item appears
4. Delete bookmark — Hover a row → click the 🗑️ icon → item disappears
5. Persistence — Reload the page and confirm added/deleted bookmarks are preserved in localStorage
6. Browser Bookmarks — Confirm the "Browser Bookmarks" section is not shown in dev mode (correct — Chrome API unavailable)
7. Light theme — Click the theme toggle to switch to light mode; confirm all card backgrounds, text, buttons, and borders are clearly visible with proper contrast
8. Dark theme — Switch back and confirm dark mode appearance is unchanged

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Checklist

• I linked the related issue, if one exists.
• I assigned myself before opening the PR, if required.
• npm run lint passes.
• npm run typecheck passes.
• npm run build succeeds.
• I reviewed my own changes before requesting review.
• I did not change unrelated files.
• I updated documentation if needed.