feat: redesign LinksGrid with semantic theming, rounded corners, and new layout

- Use semantic CSS variables (--color-surface, --shadow-sm, etc.) instead
  of hardcoded Nord values and manual dark mode overrides
- Add border-radius and overflow:hidden for rounded card corners
- Move icon fill variables (--grid-fill-*) into app.css theme system:
  colorful (red/orange/green) in light, cool blues in dark
- Mottled fill distribution via prime-offset nth-child selectors
- Reorder homepage links: Recipes, Shopping, Fitness, Faith, Tasks first
- Add Nutrition direct link with heart-pulse icon
- Document site-wide design language in CLAUDE.md

src/app.css

@@ -152,6 +152,12 @@
 
 	/* Shopping icon filter — white PNGs need invert in light mode */
 	--shopping-icon-filter: invert(1);
+
+	/* LinksGrid icon fills — colorful in light */
+	--grid-fill-base: var(--nord10);
+	--grid-fill-pop-a: var(--nord11);
+	--grid-fill-pop-b: var(--nord12);
+	--grid-fill-pop-c: var(--nord14);
 }
 
 /* ============================================
@@ -217,6 +223,12 @@
 		--color-link-hover: var(--nord7);
 
 		--shopping-icon-filter: none;
+
+		/* LinksGrid icon fills — cool blues/whites in dark */
+		--grid-fill-base: var(--nord8);
+		--grid-fill-pop-a: var(--nord9);
+		--grid-fill-pop-b: var(--nord7);
+		--grid-fill-pop-c: var(--nord4);
 	}
 }
 
@@ -268,6 +280,11 @@
 	--color-link-hover: var(--nord7);
 
 	--shopping-icon-filter: none;
+
+	--grid-fill-base: var(--nord8);
+	--grid-fill-pop-a: var(--nord9);
+	--grid-fill-pop-b: var(--nord7);
+	--grid-fill-pop-c: var(--nord4);
 }
 
 /* ============================================