Introduces a light theme alongside the existing dark Obsidian Control
look, plus a sun/moon toggle in the sidebar footer.
The dashboard's CSS already drove every surface through custom
properties on :root, so the light theme is added as a second token set
under `:root[data-theme="light"]` and, in parallel, inside a
`@media (prefers-color-scheme: light)` block guarded by
`:not([data-theme="dark"])`. Net effect:
- A user with no stored preference gets their OS theme via the media
query (no flash, no JS required).
- A user who clicked the toggle gets `data-theme="light|dark"` set on
`<html>`, which wins over the media query.
The toggle component (`theme_toggle.rs`) reads `localStorage` first
then `prefers-color-scheme` on mount, and writes both the DOM
attribute and `localStorage` on click. All `web_sys` calls are gated
behind `#[cfg(feature = "web")]` so the server build stays clean.
Three CSS rules that hardcoded near-black hex values (the page dot
grid, `.code-block`, and the graph stabilization overlay) get explicit
light-mode overrides so they don't render as dark patches on white.
web-sys feature list extended with Storage, MediaQueryList, and
Element so the toggle can read the media query and set the attribute.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Sharang Parnerkar