refactor: replace hardcoded rgba/hex colors with Tailwind tokens

- rgba(255,255,255,0.xx) → bg-white/[0.xx], border-white/[0.xx]
- rgba(6,182,212,0.3) → border-primary/30 (focus states)
- #0a0a0a → bg-background
- Inline style hex colors → var(--color-primary), var(--color-brand-gradient-to)
- 28 files updated, zero hardcoded rgba() patterns remaining

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/procedural/IntakeFormModal.tsx

@@ -213,7 +213,7 @@ export function IntakeFormModal({ isOpen, fields, treeName, onSubmit, onCancel }
 
   return (
     <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/60 backdrop-blur-xs">
-      <div className="mx-4 w-full max-w-lg rounded-2xl border border-border bg-[#0a0a0a] shadow-xl">
+      <div className="mx-4 w-full max-w-lg rounded-2xl border border-border bg-background shadow-xl">
         {/* Header */}
         <div className="border-b border-border px-6 py-4">
           <h2 className="text-lg font-semibold text-foreground">Project Information</h2>