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/migration_registry.txt

@@ -7,3 +7,4 @@
 20261103074807107-initial
 20261103074902604-sittings
 20261103130213716-dreams
+20261103143338267-library