detector: hero pulsing-dot promotion, nav-CTA contrast gap closure, shape-assembled-illustration (56 -> 57)

Item 1 (hero liveness theater):
- pulsing-dot now merges declarations per selector across rule blocks
  (cascade-approximate), descends into media queries, and strips
  prefers-reduced-motion: reduce overrides before the predicate runs.
  Catches the shipped split-block constructions (size in the base rule,
  animation added later or inside a no-preference media block).
- Dots whose element sits inside a header/nav landmark are promoted to
  error severity (string-level landmark ranges in both engines); the
  browser engine additionally promotes dots resting in the first ~900px.
- blinking-cursor findings in the first ~900px or inside header/nav are
  promoted from advisory to warning.
- Per-finding severity overrides now flow through static-html,
  browser-injected serialization, and detect-url.

Item 2 (nav-CTA contrast constructions):
- The a24-opus 01/002 header CTA already fires (specificity cascade +
  oklch + var() all resolved); systematic sweep found two remaining
  escapes and closes both:
  - own gradient background on a SAFE_TAGS element (checkColors styled-
    control exception now treats an own gradient as an own surface,
    contrast measured against the worst stop)
  - ::before/::after full-cover surface (static cascade marks pseudo
    surfaces; browser adapter reads the pseudo computed style) so text is
    measured against the surface the browser actually paints
- nav-cta-constructions fixture locks all eight computable construction
  families; background-image: url() remains unflaggable by design.

Item 3 (shape-assembled-illustration, slop/advisory):
- New rule for large inline SVGs composing a pictorial scene from >= 8
  primitive shapes at >= 200x200 intrinsic size with >= 3 distinct fills.
  Charts (axis labels), stroke-only technical drawings, icons/logos
  (small explicit size), and pattern-tiled backgrounds are exempt.
  1.8 percent fire rate over the 3069-sample eval corpus, all verified
  pictorial scenes; zero fires across val-a22/val-a24.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

cli/engine/engines/browser/detect-url.mjs

@@ -254,7 +254,7 @@ async function detectUrl(url, options = {}) {
         return window.impeccableDetect({ decorate: false, serialize: true });
       });
       return serializedGroups.flatMap(({ findings }) =>
-        findings.map(f => ({ id: f.type, snippet: f.detail, ignoreValue: f.ignoreValue || '' }))
+        findings.map(f => ({ id: f.type, snippet: f.detail, ignoreValue: f.ignoreValue || '', severity: f.severity || '' }))
       );
     });
     // Content invisible at rest: reveal sweep, then re-measure. Runs after
@@ -298,6 +298,9 @@ async function detectUrl(url, options = {}) {
   return filterByProviders(results.map(f => {
     const item = finding(f.id, url, f.snippet);
     if (f.ignoreValue) item.ignoreValue = f.ignoreValue;
+    // Per-finding severity promotion (e.g. hero-region pulsing dot)
+    // overrides the registry default carried by finding().
+    if (f.severity && f.severity !== item.severity) item.severity = f.severity;
     return item;
   }), options.providers);
 }