build(deploy)!: the instance's compose file is compose.learn.yaml, beside compose.train.yaml and compose.todo.yaml

No file has Compose's default name any more, so .env's COMPOSE_FILE is always set,
naming compose.learn.yaml first (.env.example sets it). compose.yaml stays as a link to
compose.learn.yaml for the one deploy that switches learn.halkyon.eu's .env over: the
deploy's merge runs with the COMPOSE_FILE from before. A later commit removes it.

BREAKING CHANGE: an instance's deploy/.env must set COMPOSE_FILE, starting with
compose.learn.yaml, before the link goes.

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/lib/src/dictionary/dictionary_reload_future_call.dart

@@ -3,7 +3,7 @@ import 'package:halkyon_learn_server/src/dictionary/dictionary_loader.dart';
 import 'package:serverpod/serverpod.dart';
 
 /// Rereads the dictionary folder and loads the files that changed: the
-/// dictionaries service replaces them weekly (`deploy/compose.yaml`); the
+/// dictionaries service replaces them weekly (`deploy/compose.learn.yaml`); the
 /// server schedules it hourly when it starts (`server.dart`): an hour
 /// with nothing changed costs it a hash of each file.
 class DictionaryReloadFutureCall extends FutureCall {