fix(map): the hero map's fade to the header was hardcoded white

The fade between the map band and the school header ramped through
rgba(255,255,255,...) and landed on var(--bg-card). In the light theme
that is white into white and invisible, as designed. In the dark theme
it climbed to 95% WHITE and then met a near-black card, putting a bright
band across the full width exactly where the map should dissolve into
the title.

Fading to the colour the gradient lands on is the whole trick, and it
only works if that colour is a token — so --bg-card-rgb now exists in
both theme blocks, matching the --hero-ground-rgb precedent.

Two more defects in the same file, same cause, found while in there:

The controls floating over the map paired a hardcoded white background
with color: var(--text-primary), which resolves to #E9EEF0 in dark —
near-white text on a near-white button. These deliberately do NOT follow
the theme, because the map tiles are light in both, so the ink is now
literal too and says why. A themed token is the wrong tool for a surface
that never changes.

The loading skeleton swept 50% white across var(--bg-secondary), which
is a bright flash every 1.4s on a dark page. It now sweeps toward the
card colour, a shade lighter than the ground in both themes.

The guard is a stylesheet test rather than a render test, because the
bug is invisible in the theme it was written for. Verified by reverting
each fix in turn: it names .fade and .openHint exactly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

nextjs-app/components/SchoolHeroMap.module.css

@@ -47,7 +47,13 @@
     width: 100%;
     height: 100%;
     background:
-        linear-gradient(100deg, rgba(255, 255, 255, 0) 40%, rgba(255, 255, 255, .5) 50%, rgba(255, 255, 255, 0) 60%) var(--bg-secondary);
+        /* Sweeps toward the card colour, which is a shade lighter than this
+           ground in both themes. Hardcoded white was a bright flash across a
+           dark page every 1.4s while the tiles loaded. */
+        linear-gradient(100deg,
+            rgba(var(--bg-card-rgb), 0) 40%,
+            rgba(var(--bg-card-rgb), .5) 50%,
+            rgba(var(--bg-card-rgb), 0) 60%) var(--bg-secondary);
     background-size: 200% 100%;
     animation: shimmer 1.4s infinite;
 }
@@ -76,6 +82,15 @@
     justify-content: center;
 }
 
+/*
+ * Controls that float ON the map.
+ *
+ * The map tiles are light in both themes, so these deliberately do NOT follow
+ * the theme — they follow the map. The literal ink below is the point: paired
+ * with a hardcoded white background, `color: var(--text-primary)` resolved to
+ * #E9EEF0 in the dark theme and put near-white text on a near-white button.
+ * A themed token is the wrong tool for a surface that never changes.
+ */
 .openHint {
     display: inline-flex;
     align-items: center;
@@ -85,7 +100,8 @@
     border-radius: 999px;
     font-size: 13px;
     font-weight: 600;
-    color: var(--text-primary);
+    /* See "Controls that float ON the map" above. */
+    color: #1C2731;
     background: rgba(255, 255, 255, .85);
     -webkit-backdrop-filter: blur(6px);
     backdrop-filter: blur(6px);
@@ -113,11 +129,18 @@
        on top of the blend. */
     z-index: 450;
     pointer-events: none;
+    /* The card colour, not white.
+       This ramp was hardcoded white and ended at var(--bg-card). In the light
+       theme that is white into white and invisible, as intended. In the dark
+       theme it climbed to 95% WHITE and then met a near-black card — a bright
+       band across the full width, right where the map is supposed to dissolve
+       into the header. Fading to the same colour the gradient lands on is the
+       whole trick, and it only works if that colour is a token. */
     background: linear-gradient(to bottom,
-            rgba(255, 255, 255, 0) 0%,
-            rgba(255, 255, 255, .35) 35%,
-            rgba(255, 255, 255, .75) 62%,
-            rgba(255, 255, 255, .95) 82%,
+            rgba(var(--bg-card-rgb), 0) 0%,
+            rgba(var(--bg-card-rgb), .35) 35%,
+            rgba(var(--bg-card-rgb), .75) 62%,
+            rgba(var(--bg-card-rgb), .95) 82%,
             var(--bg-card) 100%);
 }
 
@@ -134,7 +157,8 @@
     border: none;
     border-radius: 8px;
     background: rgba(255, 255, 255, .92);
-    color: var(--text-primary);
+    /* See "Controls that float ON the map" above. */
+    color: #1C2731;
     cursor: pointer;
     box-shadow: 0 2px 10px rgba(var(--shadow-rgb), .2);
 }