fix(preview): stop spec generation timing out behind the edge proxy

The /v1/servers/preview route ran claude-opus-4-7 synchronously; full spec
generation routinely exceeded Cloudflare's ~100s proxy cap, so the browser
received a headerless 524 and reported it as a CORS failure.

- preview now uses claude-sonnet-4-6 with a 45s per-attempt timeout and one
  retry — comfortably inside the proxy budget
- generateSpec maps an exhausted timeout to SpecTimeoutError; the route
  returns a clean 504 (with CORS headers) instead of a stalled connection
- analyze step: live elapsed-seconds counter as freeze-proof, plus a
  reduced-motion exception so the loading spinner keeps spinning (a status
  indicator, which WCAG exempts from reduced-motion)
- textarea resize grip restyled to dark theme (light hatch on dark square)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/app/globals.css

@@ -87,6 +87,17 @@
   ::-webkit-scrollbar-thumb:hover {
     background: var(--color-fg-subtle);
   }
+  /* Textarea resize grip — light hatching on a dark square so it matches the
+     theme instead of the OS default (light square with dark hatching). */
+  textarea::-webkit-resizer {
+    background-color: var(--color-bg);
+    background-image: repeating-linear-gradient(
+      -45deg,
+      var(--color-fg-muted) 0 1px,
+      transparent 1px 4px
+    );
+    border-bottom-right-radius: var(--radius-md);
+  }
 }
 
 @layer components {
@@ -115,6 +126,16 @@
       transition-duration: 0.001ms !important;
     }
   }
+  /* A loading spinner reports system status — WCAG treats status indicators as
+     an exception to reduced-motion, so keep it spinning after the rule above
+     has damped every decorative animation. Same layer + higher specificity
+     than the universal selector, so this !important wins. */
+  @media (prefers-reduced-motion: reduce) {
+    .animate-spin {
+      animation-duration: 1s !important;
+      animation-iteration-count: infinite !important;
+    }
+  }
 }
 
 @keyframes pulse-dot {