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>