fix(app): the app has its own icon instead of Flutter's

The launcher showed Flutter's logo: the project template's icons were
never replaced. tool/app_icons.py now makes every icon from the
kingfisher (assets/icon/halkyon_icon.png), through flutter_launcher_icons
v0.14.4 configured in the app's pubspec: Android's adaptive icon (the
kingfisher inset 16 % on white, for each launcher to cut to its shape)
and the square one before Android 8; iOS's, without transparency;
macOS's, the rounded tile on Apple's grid (824 of 1024 pixels); and
Windows', the rounded tile, its .ico with every size from 16 to 256
pixels (the tool writes only 256). It keeps the iOS project file as it
was, which the tool would break (flutter_launcher_icons issue 634), and
writes the snap's icon as tool/snap_icon.py did, which it replaces.

The Linux runner gives its window the bundled icon too, for desktops
that don't take it from the desktop file.

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

halkyon_learn_flutter/pubspec.yaml

@@ -92,6 +92,9 @@ 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).
+  flutter_launcher_icons: ^0.14.4
   flutter_test:
     sdk: flutter
   # A test drives sign-in through its front, as Serverpod's GitHub sign-in does.
@@ -156,3 +159,25 @@ flutter:
   #
   # For details regarding fonts from package dependencies,
   # see https://flutter.dev/custom-fonts/#from-packages
+
+# 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
+# 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"
+  android: true
+  adaptive_icon_background: "#ffffff"
+  adaptive_icon_foreground: "assets/icon/halkyon_icon.png"
+  ios: true
+  remove_alpha_ios: true
+  background_color_ios: "#ffffff"
+  macos:
+    generate: true
+    image_path: "build/icons/macos.png"
+  windows:
+    generate: true
+    image_path: "build/icons/rounded.png"
+    icon_size: 256