feat(ui): Lucide migration unit 1 — dependency + heart (#60)

Design system mandates Lucide, not Material. Foundation before the
mechanical Icons.* sweep:

- pubspec: add flutter_lucide ^1.11.0
- shared/widgets/lucide_heart.dart: LucideHeart renders the verified
  lucide-icons/lucide heart path as outline (stroke) or filled, via
  flutter_svg, tinted by color — Lucide ships no filled heart, so the
  liked state fills the same Lucide silhouette (user-chosen approach)
- like_button: use LucideHeart instead of Icons.favorite/_border
- notification drawables re-derived from the verbatim Lucide heart
  path (border = stroke, filled = fill); separators spaced for
  Android pathData

Unit 2 (mechanical Icons.* -> LucideIcons.* sweep) follows once this
is CI-green. pubspec.lock regenerated by CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/android/app/src/main/res/drawable/ic_stat_favorite.xml

@@ -4,7 +4,8 @@
     android:viewportWidth="24"
     android:viewportHeight="24"
     android:tint="#FFFFFFFF">
+  <!-- Lucide "heart" (filled) — same path verbatim from lucide-icons/lucide -->
   <path
       android:fillColor="#FFFFFFFF"
-      android:pathData="M12,21.35l-1.45,-1.32C5.4,15.36 2,12.28 2,8.5 2,5.42 4.42,3 7.5,3c1.74,0 3.41,0.81 4.5,2.09C13.09,3.81 14.76,3 16.5,3 19.58,3 22,5.42 22,8.5c0,3.78 -3.4,6.86 -8.55,11.54L12,21.35z"/>
+      android:pathData="M2 9.5a5.5 5.5 0 0 1 9.591 -3.676 .56 .56 0 0 0 .818 0A5.49 5.49 0 0 1 22 9.5c0 2.29 -1.5 4 -3 5.5l-5.492 5.313a2 2 0 0 1 -3 .019L5 15c-1.5 -1.5 -3 -3.2 -3 -5.5"/>
 </vector>

flutter_client/android/app/src/main/res/drawable/ic_stat_favorite_border.xml

@@ -4,7 +4,12 @@
     android:viewportWidth="24"
     android:viewportHeight="24"
     android:tint="#FFFFFFFF">
+  <!-- Lucide "heart" (outline) — path verbatim from lucide-icons/lucide -->
   <path
-      android:fillColor="#FFFFFFFF"
-      android:pathData="M16.5,3c-1.74,0 -3.41,0.81 -4.5,2.09C10.91,3.81 9.24,3 7.5,3 4.42,3 2,5.42 2,8.5c0,3.78 3.4,6.86 8.55,11.54L12,21.35l1.45,-1.32C18.6,15.36 22,12.28 22,8.5 22,5.42 19.58,3 16.5,3zM12.1,18.55l-0.1,0.1 -0.1,-0.1C7.14,14.24 4,11.39 4,8.5 4,6.5 5.5,5 7.5,5c1.54,0 3.04,0.99 3.57,2.36h1.87C13.46,5.99 14.96,5 16.5,5c2,0 3.5,1.5 3.5,3.5 0,2.89 -3.14,5.74 -7.9,10.05z"/>
+      android:strokeColor="#FFFFFFFF"
+      android:strokeWidth="2"
+      android:strokeLineCap="round"
+      android:strokeLineJoin="round"
+      android:fillColor="#00000000"
+      android:pathData="M2 9.5a5.5 5.5 0 0 1 9.591 -3.676 .56 .56 0 0 0 .818 0A5.49 5.49 0 0 1 22 9.5c0 2.29 -1.5 4 -3 5.5l-5.492 5.313a2 2 0 0 1 -3 .019L5 15c-1.5 -1.5 -3 -3.2 -3 -5.5"/>
 </vector>

flutter_client/lib/likes/like_button.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../api/endpoints/likes.dart';
+import '../shared/widgets/lucide_heart.dart';
 import '../theme/theme_extension.dart';
 import 'likes_provider.dart';
 
@@ -25,8 +26,8 @@ class LikeButton extends ConsumerWidget {
       orElse: () => false,
     );
     return IconButton(
-      icon: Icon(
-        liked ? Icons.favorite : Icons.favorite_border,
+      icon: LucideHeart(
+        filled: liked,
         color: liked ? fs.accent : fs.ash,
         size: size,
       ),

flutter_client/lib/shared/widgets/lucide_heart.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_svg/flutter_svg.dart';
+
+/// The Lucide "heart" silhouette rendered as either an outline (stroke)
+/// or a solid fill. Lucide ships only an outline heart, so the liked
+/// state fills the same authoritative Lucide path (verified verbatim
+/// from lucide-icons/lucide) — keeping both states visually Lucide
+/// rather than introducing a Material filled heart. Used by LikeButton
+/// (and, re-derived to a VectorDrawable, by the media notification).
+class LucideHeart extends StatelessWidget {
+  const LucideHeart({
+    required this.filled,
+    required this.color,
+    this.size = 22,
+    super.key,
+  });
+
+  final bool filled;
+  final Color color;
+  final double size;
+
+  static const _path =
+      'M2 9.5a5.5 5.5 0 0 1 9.591-3.676.56.56 0 0 0 .818 0A5.49 5.49 0 0 1 '
+      '22 9.5c0 2.29-1.5 4-3 5.5l-5.492 5.313a2 2 0 0 1-3 .019L5 15c-1.5-1.5'
+      '-3-3.2-3-5.5';
+
+  @override
+  Widget build(BuildContext context) {
+    final svg = filled
+        ? '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">'
+            '<path d="$_path" fill="currentColor"/></svg>'
+        : '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">'
+            '<path d="$_path" fill="none" stroke="currentColor" '
+            'stroke-width="2" stroke-linecap="round" '
+            'stroke-linejoin="round"/></svg>';
+    return SvgPicture.string(
+      svg,
+      width: size,
+      height: size,
+      colorFilter: ColorFilter.mode(color, BlendMode.srcIn),
+    );
+  }
+}

flutter_client/pubspec.yaml

@@ -22,6 +22,9 @@ dependencies:
   flutter_secure_storage: ^10.1.0
   go_router: ^17.2.3
   flutter_svg: ^2.0.16
+  # Lucide icon set (design system mandates Lucide, not Material).
+  # Icons exposed as LucideIcons.<snake_case> IconData usable in Icon().
+  flutter_lucide: ^1.11.0
   google_fonts: ^8.1.0
   # 10.x conflicts with flutter_secure_storage 10.x on win32. Hold at 8.3.1
   # until either lib bumps win32 to 6.x.