chore(web): document set-state-in-effect on ThemeToggle localStorage read (#90)

ThemeToggle's mount effect reads localStorage then setTheme, a pattern
react-hooks/set-state-in-effect flags. It is safe here: localStorage is
SSR-unavailable so the read must happen post-mount, and ThemeScript
already applies the dark class before hydration (no page FOUC). Add a
targeted eslint-disable-next-line with justification.

web/ lint is now green (0 errors).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/components/ThemeToggle.tsx

@@ -12,6 +12,11 @@ export function ThemeToggle() {
 
   useEffect(() => {
     const stored = localStorage.getItem("sl-theme") as Theme | null;
+    // localStorage is unavailable during SSR, so the stored theme can only be
+    // read post-mount. ThemeScript already applies the `dark` class before
+    // hydration (no page FOUC); only the toggle icon corrects on mount. The
+    // rule is a false positive for this hydration-from-localStorage read.
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     if (stored) setTheme(stored);
   }, []);