feat: storage writes via storage-agent, accepts_uploads and write_template (M5.5)

- storage-agent: POST /internal/files copies a staged file into a source
  (temp file, fsync, SHA-256 check, hard link so nothing is overwritten,
  " (2)" suffix on conflict, owner PIPU_FILE_UID/GID) and
  POST /internal/files/test. NFS sources that accept uploads are mounted
  rw in an agent-only /library-rw and bind-mounted read-only for others;
  local sources are written through /library-host-rw.
- meta: write templates ({track:02}, {disc:1-}, [optional]) with name
  sanitising and length limits, suggestion from the source's regexes
  and a reversibility check against 50 catalogue tracks.
- API and admin UI: accepts_uploads / write_template on sources,
  write-template suggest and check endpoints, write test result.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/i18n/locales/ru/errors.json

@@ -47,7 +47,8 @@
     "source_type_invalid": "Неизвестный тип хранилища",
     "query_empty": "Введите запрос",
     "wave_activity_invalid": "Неизвестное занятие",
-    "wave_mood_invalid": "Неизвестное настроение"
+    "wave_mood_invalid": "Неизвестное настроение",
+    "template_invalid": "Неверный шаблон пути: {{reason}}"
   },
   "users": {
     "not_found": "Пользователь не найден",
@@ -56,7 +57,8 @@
   "library": {
     "source_not_found": "Хранилище не найдено",
     "scan_running": "Скан уже идёт",
-    "source_offline": "Хранилище не подключено"
+    "source_offline": "Хранилище не подключено",
+    "template_unavailable": "Не удалось подобрать шаблон: ни один регэксп хранилища не переводится в шаблон или в хранилище нет файлов"
   },
   "catalog": {
     "not_found": "Не найдено"