Upgrade Docsy theme from v0.2.0 to v0.12.0 and implement Bootstrap 5 dark mode.

Core Changes:
- Enable showLightDarkModeMenu in config.toml
- Add theme toggle component to navbar (light/dark/auto modes)
- Store user preference in localStorage
- Respect prefers-color-scheme media query

Styling Implementation:
- Use Bootstrap 5 CSS variables (--bs-body-color, --bs-secondary-bg, etc.) for all UI elements
- Style navbar, header, sidebar, tables, admonitions, and forms for dark mode
- Add Pygments-generated GitHub Dark theme for code syntax highlighting in Sphinx docs
- Adapt confetti animation to dynamically set background based on theme
- Ensure proper semantic colors for all admonition types (note, warning, error, hint, etc.)

Technical Details:
- Added $td-sidebar-tree-root-color variable (required by Docsy v0.2.0+)
- Added $font-awesome-font-name variable (required by Docsy v0.6.0+)
- Added .-bg-orange utility class (required by Docsy v0.6.0+)
- Created pygments/_dark.scss (generated via: pygmentize -S github-dark)
- Use hooks/body-end.html for webpack scripts (proper Docsy pattern)
- Add dark mode support to Sphinx theme (header.html, layout.html)
- Update .gitignore to exclude site/public/ directory

Fixed Issues:
- Confetti animation now visible with transparent header background
- Sidebar links readable in dark mode (increased contrast)
- All admonition types (including seealso) properly colored
- Logo text white in dark mode
- Navbar and header backgrounds adapt to theme

Architecture:
- Removed baseof.html override, use Docsy hooks instead
- Follow Docsy best practices for customization
- Use CSS variables for maintainability

Testing:
- Verified dark mode toggle works on all pages
- Confirmed confetti animation adapts to theme changes
- Tested all admonition types in light and dark modes
- Verified code syntax highlighting in Sphinx documentation

Fix CSS lint errors and add dark mode support for blog page

- Replace hardcoded colors in blog page with Bootstrap CSS variables
- Fix CSS specificity linting errors in rating component
- Add stylelint disable for dark mode block where linter doesn't understand theme context

The Docsy v0.12.0 theme requires Hugo 0.146.0+ and uses Bootstrap/FontAwesome
as NPM dependencies rather than Hugo modules.

Changes:
- Upgraded Hugo from 0.135.0 to 0.146.0 (minimum required by Docsy v0.12.0)
- Added npm install step in Docsy theme directory to install Bootstrap 5.3.6
  and FontAwesome 6.7.2 from theme's package.json

The theme's hugo.yaml mounts these from node_modules/ directories. No Go
installation or Hugo module commands needed.

Tested with act - build completes successfully.

Custom CSS (main-custom.scss) was not being generated after upgrading
Docsy from v0.2.0-pre to v0.12.0.

Root cause:
Docsy v0.12.0 has layouts/_partials/head.html which Hugo prioritizes
over our layouts/partials/head.html, so our CSS processing wasn't called.

Fix:
- Add layouts/_partials/head.html to override Docsy's template
- Add layouts/_partials/head-css.html (must exist in same directory)
- Remove CSS processing from head-end.html hook (moved to head-css.html)

- Add dark-mode overrides for Docsy/Sphinx left sidebar (CONTENT) toctree links