Halkyon's shared packages

A pub workspace of the Dart packages Halkyon's apps share: halkyon_ui,
Halkyon's look (the theme, fonts, layout and shared widgets, with texts
in English and German), halkyon_core's low-level primitives and
halkyon_interop's cross-app contracts. Dart 3.13 with LeanCode's lints,
configured once at the root; apps take a package by git, pinned to a
signed commit.

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

packages/halkyon_ui/l10n.yaml

@@ -0,0 +1,14 @@
+# Flutter's gen-l10n: the strings in lib/l10n/*.arb become HalkyonUiLocalizations,
+# generated into lib/l10n/halkyon_ui_localizations*.dart (committed, never edited or
+# formatted by hand, as apps take this package by git). halkyon_ui_en.arb, the
+# template, is British English, also the fallback; halkyon_ui_en_US.arb overrides
+# what American English spells differently; halkyon_ui_en_GB.arb is empty; German
+# says "du".
+arb-dir: lib/l10n
+template-arb-file: halkyon_ui_en.arb
+output-dir: lib/l10n
+output-localization-file: halkyon_ui_localizations.dart
+output-class: HalkyonUiLocalizations
+# `HalkyonUiLocalizations.of(context).foo` without a `!`: apps install the
+# delegate.
+nullable-getter: false