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/bin/check_library.dart

@@ -0,0 +1,29 @@
+import 'dart:io';
+
+import 'package:halkyon_meditate_server/src/library/library_manifest.dart';
+
+/// Checks an operator's library folder before it is deployed (ADR 0038,
+/// D16), as the server reads it: what it would serve, and every item,
+/// course and category it would refuse, with the reason. Exits 1 where
+/// anything is refused, 64 without a folder.
+///
+///     dart run bin/check_library.dart /srv/meditate-library
+void main(List<String> args) {
+  if (args.length != 1) {
+    stderr.writeln('Usage: dart run bin/check_library.dart <library folder>');
+    exitCode = 64;
+    return;
+  }
+  final library = readLibrary(Directory(args.single));
+  for (final problem in library.problems) {
+    stdout.writeln('✗ $problem');
+  }
+  stdout.writeln(
+    '${library.items.length} items, ${library.courses.length} courses and '
+    '${library.categories.length} categories of its own would be served; '
+    '${library.problems.length} problems.',
+  );
+  if (library.problems.isNotEmpty) {
+    exitCode = 1;
+  }
+}