## 1. Theme Persistence Across Visits

- [x] 1.1 Add cookie helpers in `site/src/layouts/BaseLayout.astro` to read/write a `site_theme` cookie (Path=/, SameSite=Lax, 1y TTL; Secure on HTTPS)
- [x] 1.2 Update the head theme-init script in `site/src/layouts/BaseLayout.astro` to prefer localStorage, then cookie, then environment signals
- [x] 1.3 Update the theme setter in `site/src/layouts/BaseLayout.astro` to keep localStorage and cookie in sync on user selection (cookie fallback when localStorage throws)

## 2. Umami Tracking For Theme Switch

- [x] 2.1 Define event emission on user-initiated theme changes using `window.umami.track("theme_switch", ...)` (guarded when Umami is missing)
- [x] 2.2 Use taxonomy fields for the event payload: `target_id=theme.switch.<theme>`, `placement=theme_notch`, include `theme` and `prev_theme` when available
- [x] 2.3 Ensure theme restoration on page load does NOT emit `theme_switch` (only explicit user interaction)

## 3. Verification

- [x] 3.1 Run `npm run build` and verify output includes cookie read fallback in the head init script
- [x] 3.2 Run `npm test` and ensure no new failures are introduced
- [x] 3.3 Manual: switch theme, reload, and confirm persistence; repeat with localStorage disabled to confirm cookie fallback