feat: full onboarding + quiz flow (Flutter from scratch)

- splash → intro → 5-step quiz → result screen
- Plus Jakarta Sans typography, indigo brand system
- animated quiz rows, multi-select concerns, progress bar
- Shaynee mascot reveal on result screen only
- flutter_animate for all transitions

lib/widgets/primary_button.dart

@@ -0,0 +1,66 @@
+import 'package:flutter/material.dart';
+import 'package:google_fonts/google_fonts.dart';
+import '../theme.dart';
+
+class PrimaryButton extends StatelessWidget {
+  final String label;
+  final VoidCallback onTap;
+  final bool enabled;
+  final IconData? icon;
+
+  const PrimaryButton({
+    super.key,
+    required this.label,
+    required this.onTap,
+    this.enabled = true,
+    this.icon,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      onTap: enabled ? onTap : null,
+      child: AnimatedContainer(
+        duration: const Duration(milliseconds: 200),
+        height: 56,
+        decoration: BoxDecoration(
+          gradient: enabled
+              ? const LinearGradient(
+                  colors: [SColors.primary, SColors.gradientBot],
+                  begin: Alignment.centerLeft,
+                  end: Alignment.centerRight,
+                )
+              : null,
+          color: enabled ? null : SColors.border,
+          borderRadius: BorderRadius.circular(16),
+          boxShadow: enabled
+              ? [
+                  BoxShadow(
+                    color: SColors.primary.withAlpha(60),
+                    blurRadius: 16,
+                    offset: const Offset(0, 6),
+                  )
+                ]
+              : [],
+        ),
+        child: Row(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Text(
+              label,
+              style: GoogleFonts.plusJakartaSans(
+                fontSize: 16,
+                fontWeight: FontWeight.w700,
+                color: enabled ? Colors.white : SColors.textSecondary,
+              ),
+            ),
+            if (icon != null) ...[
+              const SizedBox(width: 8),
+              Icon(icon, color: enabled ? Colors.white : SColors.textSecondary, size: 18),
+            ],
+          ],
+        ),
+      ),
+    );
+  }
+}