fix(aicoc-hub): lighter dark-mode cards & blend hero corners

Two visual tweaks based on dark-mode preview feedback:

1. **Lighter cards.** The previous #1a1a1c card bg was too close to the
   page tone — cards barely separated from the background. Bump to
   #2d2d33 with a #3d3d44 border so cards visibly lift. Text colors
   nudged slightly lighter to keep readable contrast (#f5f5f7 title,
   #d4d4d8 description).

2. **Blend the hero corners with the page.** The hero's border-radius
   was revealing the page bg (#0e0e10) at the corners, which read as
   lighter "white" patches next to the hero's #0b0b0d darkest gradient
   stop. Match the page bg to the hero's darkest tone so the rounded
   corners disappear into the page seamlessly.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: 2 people

blocks/session-card/session-card.css

@@ -195,8 +195,11 @@
  */
 @media (prefers-color-scheme: dark) {
   .session-card {
-    background: #1a1a1c;
-    border-color: #2a2a2e;
+    /* Lighter than the page bg (#0b0b0d) so cards lift visibly. The
+     * earlier #1a1a1c was too close to the page tone and the cards
+     * blended in. */
+    background: #2d2d33;
+    border-color: #3d3d44;
   }
 
   .session-card:hover,
@@ -206,28 +209,29 @@
   }
 
   .session-card-title {
-    color: #f0f0f0;
+    color: #f5f5f7;
   }
 
   .session-card-description {
-    color: #c5c5c9;
+    color: #d4d4d8;
   }
 
   .session-card-meta {
-    color: #888;
+    color: #9a9aa0;
   }
 
   .session-card-presenter {
-    color: #f0f0f0;
+    color: #f5f5f7;
   }
 
   .session-card-sep {
-    color: #555;
+    color: #666;
   }
 
-  /* Dark variant of the no-image media strip — softer border. */
+  /* Dark variant of the no-image media strip — softer border matching the
+   * lighter card body. */
   /* stylelint-disable-next-line selector-class-pattern */
   .session-card--no-image .session-card-media {
-    border-bottom-color: #2a2a2e;
+    border-bottom-color: #3d3d44;
   }
 }

styles/aicoc.css

@@ -175,11 +175,12 @@ body.aicoc-hub main > div ~ div {
   background: transparent;
 }
 
-/* Dark mode: tint the body bg so the contained dark hero still stands out
- * against the surrounding page (which would otherwise be pure white). */
+/* Dark mode: match the body bg to the hero's darkest gradient stop so the
+ * hero's rounded corners blend seamlessly with the page instead of showing
+ * lighter-grey corners. */
 @media (prefers-color-scheme: dark) {
   body.aicoc {
-    background-color: #0e0e10;
+    background-color: #0b0b0d;
   }
 }