chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

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_server/analysis_options.yaml

@@ -0,0 +1,22 @@
+# The workspace's lint rules (see ../analysis_options.yaml), minus generated code.
+include: ../analysis_options.yaml
+
+analyzer:
+  exclude:
+    - lib/src/generated/**
+    - test/integration/test_tools/serverpod_test_tools.dart
+
+# Serverpod's code generator reads this package with an analyzer that doesn't know
+# Dart v3.13's primary constructors yet, and fails on them in endpoint files ("requires
+# the 'primary-constructors' language feature"; checked again with v4.0.3). So the
+# server keeps the classic constructor and class-body syntax; switch these back on once
+# Serverpod parses it.
+linter:
+  rules:
+    empty_container_bodies: false
+    unnecessary_type_name_in_constructor: false
+    use_declaring_parameters: false
+    use_primary_constructors: false
+
+formatter:
+  trailing_commas: preserve