feat: the apps' icons as one family, drawn by one tool (ADR 0031)

tool/app_icons.py at the root replaces Learn's and Todo's scripts: each
app's Lucide glyph (lucide-static 1.50.0) drawn by librsvg, fading from
cobalt through the colours ADR 0031 names, then every platform's
launcher icon through flutter_launcher_icons, Windows' .ico with every
size, and Learn's snap icon.

Learn's icon becomes the graduation cap, its window's on Linux too, with
Lucide's notice in its licence list; the kingfisher stays the emblem on
the rail and the launch screen. Todo's becomes list-todo, Train's bike.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/pubspec.yaml

@@ -148,8 +148,9 @@ dev_dependencies:
   # Used for agents to drive the app through the Dart MCP
   flutter_driver:
     sdk: flutter
-  # Writes the app's icons for every platform from assets/icon/halkyon_icon.png, run
-  # through tool/app_icons.py (see the flutter_launcher_icons section below).
+  # Writes the app's icons for every platform from assets/icon/halkyon_learn_icon.png,
+  # run through the repository's tool/app_icons.py (see the flutter_launcher_icons
+  # section below).
   flutter_launcher_icons: ^0.14.4
   flutter_test:
     sdk: flutter
@@ -186,8 +187,12 @@ flutter:
   # https://flutter.dev/assets-and-images/#from-packages
   assets:
     - assets/config.json
-    # The kingfisher: the app icon, also shown atop the navigation rail.
+    # The kingfisher, Halkyon's emblem: atop the navigation rail and on the launch
+    # screen.
     - assets/icon/halkyon_icon.png
+    # The app's icon (ADR 0031), the window's on Linux, and Lucide's notice for it.
+    - assets/icon/halkyon_learn_icon.png
+    - assets/icon/LICENSE-lucide.txt
     # Region maps for map questions (see assets/maps/ATTRIBUTION.md).
     - assets/maps/japan_prefectures.geojson
     - assets/maps/world_countries.geojson
@@ -222,17 +227,17 @@ flutter:
       fonts:
         - asset: assets/fonts/NotoSansKR-Variable.otf
 
-# The app's icons, written by tool/app_icons.py: it prepares the images derived from
-# the kingfisher in build/icons/ first, then runs `dart run flutter_launcher_icons`
-# with this. Android: an adaptive icon, the kingfisher inset on white for each
-# launcher to cut to its shape, and the square one older Androids show. iOS: without
+# The app's icons, written by the repository's tool/app_icons.py: it prepares the
+# images derived from Lucide's graduation cap in build/icons/ first, then runs `dart
+# run flutter_launcher_icons` with this. Android: an adaptive icon, the cap on white
+# for each launcher to cut to its shape, and the square one older Androids show. iOS: without
 # transparency, as Apple requires. macOS: the rounded tile on Apple's grid. Windows:
 # the rounded tile (tool/app_icons.py then writes its .ico with every size).
 flutter_launcher_icons:
-  image_path: "assets/icon/halkyon_icon.png"
+  image_path: "assets/icon/halkyon_learn_icon.png"
   android: true
   adaptive_icon_background: "#ffffff"
-  adaptive_icon_foreground: "assets/icon/halkyon_icon.png"
+  adaptive_icon_foreground: "assets/icon/halkyon_learn_icon.png"
   ios: true
   remove_alpha_ios: true
   background_color_ios: "#ffffff"