fix(accessibility): Improve color contrast for WCAG AA compliance

Phase 4.4 Accessibility:
- Change white text to navy-dark on orange table headers (ratio 4.8:1)
- Fix subtotal rows in APU tables: orange text to navy for better contrast
- Affects styles 2, 5, 7, 10 in generic tables
- Fixes PageSpeed accessibility warnings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Assets/css/css-tablas-apu.css

@@ -214,16 +214,17 @@
 /* ========================================
    FILAS DE SUBTOTALES
    (Suma de Material, Suma de Mano de Obra, etc)
+   Fase 4.4 Accesibilidad: Color oscuro para contraste WCAG AA (4.5:1)
    ======================================== */
 .analisis table tr.subtotal-row,
 .desglose table tr.subtotal-row {
-    background-color: rgba(255, 133, 0, 0.1) !important;
+    background-color: rgba(255, 133, 0, 0.15) !important;
 }
 
 .analisis table tr.subtotal-row td,
 .desglose table tr.subtotal-row td {
     font-weight: 700;
-    color: var(--color-orange-primary);
+    color: #1e3a5f;
     padding: 0.875rem 1rem;
     border: none !important;
 }
@@ -235,7 +236,7 @@
 .analisis table tr.subtotal-row td.c6,
 .analisis table tr.subtotal-row td:nth-child(6) {
     font-size: 1.05rem;
-    color: var(--color-orange-primary);
+    color: #1e3a5f;
 }
 
 /* ========================================