feat: replace hardcoded orange hex values with blue equivalents

BrandLogo gradient, EmptyStateIllustrations SVGs, categoryColors,
landing page, brand SVG assets, and all remaining files.
Warning #eab308 → #fbbf24 (amber). categoryColors deduped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/styles/landing.css

@@ -978,7 +978,7 @@
 }
 
 .landing-pricing-card.featured {
-  border-color: #f97316;
+  border-color: #60a5fa;
   background: var(--color-bg-card);
   position: relative;
 }
@@ -1062,7 +1062,7 @@
 
 .landing-pricing-features li::before {
   content: '\2713';
-  color: #f97316;
+  color: #60a5fa;
   font-weight: 700;
   font-size: 0.8rem;
   margin-top: 2px;
@@ -1142,7 +1142,7 @@
 .landing-testimonial-quote::before {
   content: '\201C';
   font-size: 4rem;
-  color: #f97316;
+  color: #60a5fa;
   opacity: 0.3;
   vertical-align: super;
   margin-right: 1rem;
@@ -1154,7 +1154,7 @@
 .landing-testimonial-quote::after {
   content: '\201D';
   font-size: 4rem;
-  color: #f97316;
+  color: #60a5fa;
   opacity: 0.3;
   vertical-align: sub;
   margin-left: 1rem;
@@ -1227,7 +1227,7 @@
 }
 
 .landing-cta-email-input:focus {
-  border-color: #f97316;
+  border-color: #60a5fa;
   box-shadow: 0 0 0 3px rgba(96, 165, 250, 0.1);
 }