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/migrations/20260916165410927/definition_project.json

@@ -0,0 +1,24 @@
+{
+  "__className__": "serverpod.DatabaseDefinition",
+  "schemaVersion": 2,
+  "moduleName": "halkyon_learn",
+  "tables": [],
+  "installedModules": [
+    {
+      "__className__": "serverpod.DatabaseMigrationVersion",
+      "module": "serverpod",
+      "version": "20260824182259319"
+    },
+    {
+      "__className__": "serverpod.DatabaseMigrationVersion",
+      "module": "serverpod_auth_idp",
+      "version": "20260910193913364-string-rate-limit-keys"
+    },
+    {
+      "__className__": "serverpod.DatabaseMigrationVersion",
+      "module": "serverpod_auth_core",
+      "version": "20260824182354731"
+    }
+  ],
+  "migrationApiVersion": 1
+}