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/train/AGENTS.md

@@ -5,5 +5,5 @@ What holds for every app and package of this repository is in the [root AGENTS.m
 - **A shell on the shared packages**, Todo's copied and renamed (decided 2026-10-28, ADR 0030, D12; what Train is to do: ADR 0030): signing in, the instances, the account and the look work; nothing of a person's is kept or synced yet, which waits for Train's first model (ADR 0030: synced with `serverpod_offline_sync`, every row sealed, D7). Packages: `halkyon_train_server`, `halkyon_train_client` (generated, never edited), `halkyon_train_flutter`; app ID `app.halkyon.train` on every platform; no web build. Licences as Learn's (server SSPL, client and app AGPL; `LICENSE.md`).
 - **The server** includes `halkyon_base` (ADR 0014) and configures it in `server.dart` (`trainBase()`, `lib/src/train_base.dart`): its basics say it serves `train` (never change it once apps use it), sign-in mails name Halkyon Train, the source is this repository, `minimumAppBuild` 1, no data of its own to delete with a person yet (add a `deletePersonData` hook with Train's first table). Authentication through the module's builders: a password, SimpleLogin on the register, email codes proving an address, server-side sessions; no anonymous accounts (ADR 0020, D25), nor GitHub (D36). **Accounts** (ADR 0016): Train holds its own register when it runs alone, and is a member of the instance's register (Learn's server on learn.halkyon.eu) where the operator sets `ACCOUNT_REGISTER_URL` (`trainBase(accounts: AccountsMode.fromEnvironment())`) with the instance's shared `INSTANCE_SECRET` (`instanceSecret`); then sign-in, handles and profiles are the register's, the email settings are the register's alone, and an identified person's deletion goes to the register first. `addInstanceRoutes` serves the calls between the services on its web server, and the server doesn't start without the secret where it needs it. `schedulePruning` (`lib/src/pruning.dart`) keeps the module's pruning scheduled, one entry each however often the server starts (and cancels the one under the pruning's name before ADR 0020, D25): the anonymous accounts left from before daily, sign-up attempts and codes hourly, as the register the deletions its members haven't confirmed hourly, as a member the people the register no longer knows daily (each a no-op in the other mode). Session logs are never persisted, in any run mode. Migrations (2026-10-28): one initial one with Serverpod's tables, its auth modules' and the module's as they stand, nothing of Train's own (Todo's grew one by one with the module; Train starts where they ended). Tests (`test/integration/train_server_test.dart`) call the module's endpoints through the server's own dispatch (`halkyon_base.<endpoint>`), since the generated test tools expose the project's endpoints alone.
 - **The app** is halkyon_app's `InstanceGate` and `SessionGate` with Train's frame (`trainFrame`: "Train" under "Halkyon", its icon, `train.example.org`, its own sentence) and `ServerpodInstanceChecker(app: 'train')`; `TrainDependencies` (`AppDependencies<TrainPerson>`) on one instance, `TrainPerson` (empty) per person; a person's app with an empty home and the account sheet: halkyon_app's `AccountTiles` (whose account on which instance, Switch account, Sign out, Delete account, which asks first) in Train's words, and halkyon_app's About (`showAppAbout`: the source of what the instance runs, from `TrainDependencies.sourceCodeUrl`, and the licence list). Texts through gen-l10n in British English (the template), German (informal du), an empty `en_US` and `en_GB` (`test/l10n/arb_files_test.dart` keeps them in step). The look follows the system's theme mode and language until Train has settings. Countries in where an instance keeps its data are named by halkyon_app's CLDR names (`AssetCountryNames`), its language picked by halkyon_app's `resolveAppLocale`. Widget tests start Train's whole tree with halkyon_app's fakes (`test/app/train_app_test.dart`).
-- **The icon** is to be Lucide's `bike` fading from cobalt through violet and strawberry into carrot (ADR 0031). Until the icon tool for every app is decided and built (ADR 0031, *What follows*), Train carries Todo's icon (`assets/icon/halkyon_train_icon.png` and the platforms' launcher icons, copied) and no tool of its own. `registerLucideLicense` puts Lucide's notice (ISC) in the licence list.
+- **The icon** is Lucide's `bike` fading from cobalt through violet and strawberry into carrot (ADR 0031), drawn with the other apps' by the repository's `tool/app_icons.py` (`python3 -I tool/app_icons.py train` from the root): `assets/icon/halkyon_train_icon.png`, Lucide's ISC licence beside it, and every platform's launcher icon through flutter_launcher_icons. `registerLucideLicense` puts Lucide's notice in the licence list.
 - **`serverpod start`** runs in `apps/train/halkyon_train_server` (it launches the app from `lib/driver.dart`); `.mcp.json`'s `--server-dir` names it when a session works on Train. Its tests need throwaway passwords in its git-ignored `config/passwords.yaml` (`database`, `serviceSecret`, `serverSideSessionKeyHashPepper`, `emailSignInPepper`) or from the environment, as CI gives them. Train's development server has ports of its own (API 8180, Insights 8181, web 8182, PostgreSQL 8190; the app's `assets/config.json`), so it runs beside Learn's, as a member of Learn's register; its tests use `config/test.yaml`'s ports, as Learn's and Todo's do, which Melos runs one package at a time.