feat(meditate): the operator's library on the server, and a course's lessons done synced

An operator's folder (MEDITATE_LIBRARY_DIR) of recordings, pictures and a
YAML manifest, library.yaml (commented sample: library.example.yaml), read
as the server starts and every ten minutes, held in memory. Items without
a licence or credit, files outside the folder, unknown categories and
courses pointing at items not served are refused and logged; a manifest
that doesn't read keeps the library served before. bin/check_library.dart
checks a folder before deploying.

The catalogue goes to signed-in people alone (LibraryEndpoint), with a
12-hour access the server signs; the web server's /library/<served name>
serves the files to that access only, by ranges (relic's StaticHandler).
No request path reaches the file system.

lesson_done: a lesson done, sealed and synced, a row each; the migration
creates the table with its spaceId index and the cascading foreign key to
the sync engine's spaces, as dream's did. ADR 0038, D16.

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/meditate/halkyon_meditate_server/migrations/20261103143338267-library/migration.json

@@ -0,0 +1,94 @@
+{
+  "__className__": "serverpod.DatabaseMigration",
+  "actions": [
+    {
+      "__className__": "serverpod.DatabaseMigrationAction",
+      "type": "createTable",
+      "createTable": {
+        "__className__": "serverpod.TableDefinition",
+        "name": "lesson_done",
+        "dartName": "LessonDone",
+        "module": "halkyon_meditate",
+        "schema": "public",
+        "columns": [
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "id",
+            "fieldName": "id",
+            "columnType": 7,
+            "isNullable": false,
+            "columnDefault": "random_v7",
+            "dartType": "UuidValue?"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "spaceId",
+            "fieldName": "spaceId",
+            "columnType": 6,
+            "isNullable": true,
+            "dartType": "int?"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "keyId",
+            "fieldName": "keyId",
+            "columnType": 0,
+            "isNullable": true,
+            "dartType": "String?"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "payload",
+            "fieldName": "payload",
+            "columnType": 5,
+            "isNullable": false,
+            "dartType": "dart:typed_data:ByteData"
+          },
+          {
+            "__className__": "serverpod.ColumnDefinition",
+            "name": "nonce",
+            "fieldName": "nonce",
+            "columnType": 5,
+            "isNullable": true,
+            "dartType": "dart:typed_data:ByteData?"
+          }
+        ],
+        "foreignKeys": [
+          {
+            "__className__": "serverpod.ForeignKeyDefinition",
+            "constraintName": "lesson_done_fk_0",
+            "columns": [
+              "spaceId"
+            ],
+            "referenceTable": "offline_sync_spaces",
+            "referenceTableSchema": "public",
+            "referenceColumns": [
+              "id"
+            ],
+            "onUpdate": 3,
+            "onDelete": 4
+          }
+        ],
+        "indexes": [
+          {
+            "__className__": "serverpod.IndexDefinition",
+            "indexName": "lesson_done_space_idx",
+            "elements": [
+              {
+                "__className__": "serverpod.IndexElementDefinition",
+                "type": 0,
+                "definition": "spaceId"
+              }
+            ],
+            "type": "btree",
+            "isUnique": false,
+            "isPrimary": false
+          }
+        ],
+        "managed": true
+      }
+    }
+  ],
+  "warnings": [],
+  "migrationApiVersion": 1
+}