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/20261008165051407-pdf-position/migration.json

@@ -0,0 +1,56 @@
+{
+  "__className__": "serverpod.DatabaseMigration",
+  "actions": [
+    {
+      "__className__": "serverpod.DatabaseMigrationAction",
+      "type": "alterTable",
+      "alterTable": {
+        "__className__": "serverpod.TableMigration",
+        "name": "pdf_source",
+        "schema": "public",
+        "addColumns": [
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "position",
+            "fieldName": "position",
+            "columnType": 0,
+            "isNullable": false,
+            "columnDefault": "'a0'",
+            "dartType": "String"
+          }
+        ],
+        "deleteColumns": [],
+        "modifyColumns": [],
+        "addIndexes": [
+          {
+            "__className__": "serverpod.IndexDefinition",
+            "indexName": "pdf_source_studyset_idx",
+            "elements": [
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "studysetId"
+              },
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "position"
+              }
+            ],
+            "type": "btree",
+            "isUnique": false,
+            "isPrimary": false
+          }
+        ],
+        "deleteIndexes": [
+          "pdf_source_studyset_idx"
+        ],
+        "addForeignKeys": [],
+        "deleteForeignKeys": [],
+        "warnings": []
+      }
+    }
+  ],
+  "warnings": [],
+  "migrationApiVersion": 1
+}

apps/learn/halkyon_learn_server/migrations/20261008165051407-pdf-position/migration.sql

@@ -0,0 +1,51 @@
+BEGIN;
+
+--
+-- ACTION ALTER TABLE
+--
+DROP INDEX "pdf_source_studyset_idx";
+ALTER TABLE "pdf_source" ADD COLUMN "position" text NOT NULL DEFAULT 'a0'::text;
+CREATE INDEX "pdf_source_studyset_idx" ON "pdf_source" USING btree ("studysetId", "position");
+
+--
+-- MIGRATION VERSION FOR halkyon_learn
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('halkyon_learn', '20261008165051407-pdf-position', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20261008165051407-pdf-position', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod', '20260824182259319', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260824182259319', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_idp
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_idp', '20260924105404509', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105404509', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_offline_sync
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_offline_sync', '20260914143806119', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260914143806119', "timestamp" = now();
+
+--
+-- MIGRATION VERSION FOR serverpod_auth_core
+--
+INSERT INTO "serverpod_migrations" ("module", "version", "timestamp")
+    VALUES ('serverpod_auth_core', '20260924105232991', now())
+    ON CONFLICT ("module")
+    DO UPDATE SET "version" = '20260924105232991', "timestamp" = now();
+
+
+COMMIT;