feat(learn,train,todo,meditate): the icons on a white tile again, coloured by the system's theme on Android and iOS (ADR 0031, D9, D10)

D10 returns every icon to D1's white tile, D8's dark one undone, the
gradients as D5 gives them (cobalt holds about 5.7 : 1 against white).

D9 adds the variants the systems colour by their theme, all from the same
glyph at the same place, drawn by tool/app_icons.py and written into the
projects by flutter_launcher_icons: Android's monochrome layer, which
themed icons tint (Android 13 and later), and iOS's dark and tinted icons
(iOS 18 and later), the dark one keeping D8's lift of 30 % towards white
on iOS's own dark background. macOS needs an Icon Composer file made on a
Mac and keeps the plain icon until then.

Whats-New: The app's icon is white again, and takes the system's colours where Android or iOS themes its icons.
Whats-New-De: Das App-Symbol ist wieder weiß und nimmt die Farben des Systems an, wo Android oder iOS seine Symbole einfärbt.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0031-the-apps-icons.md

@@ -5,7 +5,9 @@
   developer agreeing); Meditate's comes with Meditate. **D5 (2 Nov 2026) changes D2's
   gradients**: each icon ends in its app's backdrop colour; **D6** puts Learn's icon in
   place of the kingfisher inside the app; **D7** gives Train the dumbbell, Meditate the sprout;
-  **D8 (7 Nov 2026) changes D1's white tile** to the apps' dark background, the gradients lifted.
+  **D8 (7 Nov 2026) changes D1's white tile** to the apps' dark background, the gradients lifted;
+  **D9 (9 Nov 2026)** has Android and iOS colour the icons by the system's theme, macOS later;
+  **D10 (9 Nov 2026) returns to D1's white tile**, D8's dark one undone.
 - **Builds on:** ADR 0030, D12 (Train's icon is Lucide's `bike`).
 
 ## Context
@@ -112,3 +114,39 @@ Learn's and Train's. Compared as swatches the same day.
   lift (`TILE`, `LIFT`), and the apps' pubspecs give Android's adaptive background and
   iOS's the tile's colour. Inside the apps (D6) the icon is the dark tile in light mode
   too, as on the launcher. Installed apps change their icon with their next release.
+
+- **D9 The systems colour the icons by their theme where they can** (the developer's,
+  9 Nov 2026: "Android + iOS now, macOS on a Mac"). Each icon gives the variants the
+  systems take, all from the same glyph at the same place, which `tool/app_icons.py`
+  draws into the app's `build/icons/` and flutter_launcher_icons (v0.14.4) writes into
+  the projects:
+  - **Android** (13 and later, *Themed icons*): the adaptive icon's monochrome layer
+    (`adaptive_icon_monochrome`, `drawable-*/ic_launcher_monochrome.png`, at the
+    foreground's inset of 16 %), the glyph in white on transparency, which the launcher
+    tints from the wallpaper's colours. Launchers without themed icons, or with them
+    off, show D8's icon as before.
+  - **iOS** (18 and later): a dark icon (`image_path_ios_dark_transparent`), the glyph in
+    its gradient on transparency, which iOS sets on its own dark background, and a
+    tinted one (`image_path_ios_tinted_grayscale`), the glyph in white on black, which
+    iOS colours in the tint chosen. The asset catalogue holds them as the `dark` and
+    `tinted` appearances beside D8's icon, which light mode keeps; iOS before 18 reads
+    only that one.
+  - **macOS** (26, Tahoe) colours icons only from an Icon Composer file (`.icon`), which
+    flutter_launcher_icons doesn't write and only Xcode 26 on a Mac makes; macOS's icon
+    stays D8's until then, in every look macOS gives it. Done on a Mac: the glyph as an SVG layer over
+    the tile's colour in Icon Composer, the `.icon` file in the app's `macos/Runner/`,
+    named by `ASSETCATALOG_COMPILER_APPICON_NAME`. Linux and Windows have no such
+    theming; their icons stay D8's.
+
+  No new image is committed but what the projects hold: the variants are made from the
+  glyph and D5's gradients each time, so a change of glyph or colour reaches them too.
+  Installed apps change their icon with their next release.
+
+- **D10 Every icon's tile is white again, as D1 had it** (the developer's, 9 Nov 2026:
+  "Please return to the icons with white background"), D8's dark tile undone: the
+  gradients are D5's as they are, unlifted (cobalt holds about 5.7 : 1 against white), the
+  apps' pubspecs give Android's adaptive background and iOS's white, and the icon inside
+  the apps (D6) is the white tile. D9's variants stay: Android's monochrome layer and
+  iOS's tinted icon are white glyphs as before, and iOS's dark icon, which iOS sets on
+  its own dark background, keeps D8's lift of 30 % towards white (`DARK_LIFT` in
+  `tool/app_icons.py`), so cobalt keeps above 4.5 : 1 there.