feat: Tier 2 intro polish — lottie + particles_flutter

lib/intro.dart

@@ -1,6 +1,9 @@
 import 'package:animated_text_kit/animated_text_kit.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_svg/flutter_svg.dart';
+import 'dart:math' as math;
+
+import 'package:particles_flutter/engine.dart';
 import 'package:postbox_game/james_messages.dart';
 import 'package:postbox_game/postman_james_svg.dart';
 import 'package:postbox_game/theme.dart';
@@ -28,6 +31,7 @@ class _IntroState extends State<Intro> with TickerProviderStateMixin {
 
   late AnimationController _jamesWalkController;
   late Animation<double> _jamesSlide;
+  late final List<Particle> _particles;
 
   @override
   void initState() {
@@ -39,6 +43,23 @@ class _IntroState extends State<Intro> with TickerProviderStateMixin {
     _jamesSlide = Tween<double>(begin: -1.0, end: 0.0).animate(
       CurvedAnimation(parent: _jamesWalkController, curve: Curves.easeOut),
     );
+    _particles = _buildParticles();
+  }
+
+  static List<Particle> _buildParticles() {
+    final rng = math.Random();
+    return List.generate(25, (_) {
+      final speed = 0.3 + rng.nextDouble() * 0.7;
+      final angle = rng.nextDouble() * 2 * math.pi;
+      return CircularParticle(
+        radius: 1.0 + rng.nextDouble() * 3.0,
+        color: Colors.white.withValues(alpha: 0.1 + rng.nextDouble() * 0.12),
+        velocity: Offset(
+          math.cos(angle) * speed * 30,
+          math.sin(angle) * speed * 30,
+        ),
+      );
+    });
   }
 
   @override
@@ -74,23 +95,37 @@ class _IntroState extends State<Intro> with TickerProviderStateMixin {
             colors: [royalNavy, Color(0xFF3D0C13)],
           ),
         ),
-        child: SafeArea(
-          child: Column(
-            children: [
-              Expanded(child: _buildStep()),
-              Padding(
-                padding: const EdgeInsets.all(AppSpacing.lg),
-                child: SizedBox(
-                  width: double.infinity,
-                  child: FilledButton(
-                    onPressed: _advance,
-                    child:
-                        Text(_step == _totalSteps - 1 ? 'Get started' : 'Next'),
+        child: Stack(
+          children: [
+            // Subtle floating particles behind all intro content.
+            Positioned.fill(
+              child: Particles(
+                particles: _particles,
+                height: MediaQuery.of(context).size.height,
+                width: MediaQuery.of(context).size.width,
+                boundType: BoundType.WrapAround,
+                connectDots: false,
+              ),
+            ),
+            SafeArea(
+              child: Column(
+                children: [
+                  Expanded(child: _buildStep()),
+                  Padding(
+                    padding: const EdgeInsets.all(AppSpacing.lg),
+                    child: SizedBox(
+                      width: double.infinity,
+                      child: FilledButton(
+                        onPressed: _advance,
+                        child: Text(
+                            _step == _totalSteps - 1 ? 'Get started' : 'Next'),
+                      ),
+                    ),
                   ),
-                ),
+                ],
               ),
-            ],
-          ),
+            ),
+          ],
         ),
       ),
     );

pubspec.lock

@@ -25,6 +25,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.13.2"
+  archive:
+    dependency: transitive
+    description:
+      name: archive
+      sha256: a96e8b390886ee8abb49b7bd3ac8df6f451c621619f52a26e815fdcf568959ff
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.0.9"
   args:
     dependency: transitive
     description:
@@ -544,6 +552,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.3.0"
+  lottie:
+    dependency: "direct main"
+    description:
+      name: lottie
+      sha256: c5fa04a80a620066c15cf19cc44773e19e9b38e989ff23ea32e5903ef1015950
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.3.1"
   matcher:
     dependency: transitive
     description:
@@ -592,6 +608,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.0"
+  particles_flutter:
+    dependency: "direct main"
+    description:
+      name: particles_flutter
+      sha256: "74057830f0526902cc36325b5feefbbeda88b5f8f9958cf8f24ec98eeeab36c2"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.2"
   path:
     dependency: transitive
     description:
@@ -688,6 +712,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.0.0"
+  posix:
+    dependency: transitive
+    description:
+      name: posix
+      sha256: "185ef7606574f789b40f289c233efa52e96dead518aed988e040a10737febb07"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.5.0"
   provider:
     dependency: transitive
     description:

pubspec.yaml

@@ -42,6 +42,8 @@ dependencies:
   firebase_app_check: ^0.4.2
   confetti: ^0.8.0
   flutter_staggered_animations: ^1.1.1
+  lottie: ^3.1.0
+  particles_flutter: ^2.0.2
 dev_dependencies:
   flutter_test:
     sdk: flutter