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>

services/api/internal/library/agent.go

@@ -13,11 +13,14 @@ import (
 	"pipu/api/internal/storageagent"
 )
 
-// Agent — клиент storage-agent (монтирование NFS).
+// Agent — клиент storage-agent (монтирование NFS, запись импортированных файлов).
 type Agent interface {
-	Mount(ctx context.Context, sourceID uuid.UUID, spec storageagent.NFSSpec) (storageagent.MountResult, error)
+	// Mount монтирует NFS; writable — источник принимает загрузки (ещё rw-точка, видимая только агенту).
+	Mount(ctx context.Context, sourceID uuid.UUID, spec storageagent.NFSSpec, writable bool) (storageagent.MountResult, error)
 	Unmount(ctx context.Context, sourceID uuid.UUID) error
 	Test(ctx context.Context, spec storageagent.NFSSpec) (storageagent.MountResult, error)
+	TestWrite(ctx context.Context, req storageagent.WriteTestRequest) (storageagent.WriteTestResult, error)
+	WriteFile(ctx context.Context, req storageagent.WriteRequest) (storageagent.WriteResult, error)
 }
 
 // HTTPAgent ходит в storage-agent по внутренней сети с общим секретом.
@@ -86,9 +89,28 @@ func (a *HTTPAgent) do(ctx context.Context, method, path string, body any, out a
 }
 
 // Mount реализует Agent.
-func (a *HTTPAgent) Mount(ctx context.Context, id uuid.UUID, spec storageagent.NFSSpec) (storageagent.MountResult, error) {
+func (a *HTTPAgent) Mount(ctx context.Context, id uuid.UUID, spec storageagent.NFSSpec, writable bool) (storageagent.MountResult, error) {
 	var res storageagent.MountResult
-	err := a.do(ctx, http.MethodPost, "/internal/mounts", storageagent.MountRequest{SourceID: id.String(), NFSSpec: spec}, &res)
+	err := a.do(ctx, http.MethodPost, "/internal/mounts",
+		storageagent.MountRequest{SourceID: id.String(), NFSSpec: spec, Writable: writable}, &res)
+	return res, err
+}
+
+// TestWrite реализует Agent.
+func (a *HTTPAgent) TestWrite(ctx context.Context, req storageagent.WriteTestRequest) (storageagent.WriteTestResult, error) {
+	var res storageagent.WriteTestResult
+	err := a.do(ctx, http.MethodPost, "/internal/files/test", req, &res)
+	return res, err
+}
+
+// WriteFile реализует Agent. Копирование большого файла по NFS может идти минуты — отдельный таймаут.
+func (a *HTTPAgent) WriteFile(ctx context.Context, req storageagent.WriteRequest) (storageagent.WriteResult, error) {
+	var res storageagent.WriteResult
+	ctx, cancel := context.WithTimeout(ctx, 30*time.Minute)
+	defer cancel()
+	c := *a
+	c.Client = &http.Client{}
+	err := c.do(ctx, http.MethodPost, "/internal/files", req, &res)
 	return res, err
 }