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/handler.go

@@ -63,7 +63,7 @@ func (h *Handler) sourceDTO(s Source) gen.Source {
 		Id: s.ID, Name: s.Name, Type: gen.SourceType(s.Type), NfsServer: s.NFSServer, NfsExport: s.NFSExport,
 		NfsOptions: s.NFSOptions, LocalPath: s.LocalPath, TagPriority: gen.TagsFirst,
 		Status: gen.SourceStatus(s.Status), StatusMessage: s.StatusMessage, LastScanAt: s.LastScanAt,
-		CreatedAt: s.CreatedAt,
+		CreatedAt: s.CreatedAt, AcceptsUploads: s.AcceptsUploads, WriteTemplate: s.WriteTemplate,
 	}
 	if !s.TagsFirst {
 		out.TagPriority = gen.PathFirst
@@ -118,6 +118,7 @@ func (h *Handler) CreateSource(ctx context.Context, req gen.CreateSourceRequestO
 	src, err := h.svc.CreateSource(ctx, SourceInput{
 		Name: &b.Name, Type: SourceType(b.Type), NFSServer: b.NfsServer, NFSExport: b.NfsExport, NFSOptions: b.NfsOptions,
 		LocalPath: b.LocalPath, TagsFirst: tagsFirst(b.TagPriority), ScanIntervalMinutes: b.ScanIntervalMinutes,
+		AcceptsUploads: b.AcceptsUploads, WriteTemplate: b.WriteTemplate,
 	})
 	if err != nil {
 		return nil, err
@@ -140,6 +141,7 @@ func (h *Handler) UpdateSource(ctx context.Context, req gen.UpdateSourceRequestO
 	src, err := h.svc.UpdateSource(ctx, req.Id, SourceInput{
 		Name: b.Name, NFSServer: b.NfsServer, NFSExport: b.NfsExport, NFSOptions: b.NfsOptions, LocalPath: b.LocalPath,
 		TagsFirst: tagsFirst(b.TagPriority), ScanIntervalMinutes: b.ScanIntervalMinutes, Enabled: b.Enabled,
+		AcceptsUploads: b.AcceptsUploads, WriteTemplate: b.WriteTemplate,
 	})
 	if err != nil {
 		return nil, err
@@ -161,7 +163,46 @@ func (h *Handler) TestSource(ctx context.Context, req gen.TestSourceRequestObjec
 	if err != nil {
 		return nil, err
 	}
-	return gen.TestSource200JSONResponse{Ok: r.OK, Message: r.Message, AudioFiles: r.AudioFiles}, nil
+	out := gen.TestSource200JSONResponse{Ok: r.OK, Message: r.Message, AudioFiles: r.AudioFiles}
+	if r.Write != nil {
+		out.WriteOk, out.WriteMessage = &r.Write.OK, &r.Write.Message
+	}
+	return out, nil
+}
+
+// SuggestWriteTemplate реализует gen.StrictServerInterface.
+func (h *Handler) SuggestWriteTemplate(ctx context.Context, req gen.SuggestWriteTemplateRequestObject) (gen.SuggestWriteTemplateResponseObject, error) {
+	tpl, err := h.svc.SuggestWriteTemplate(ctx, req.Id)
+	if err != nil {
+		return nil, err
+	}
+	return gen.SuggestWriteTemplate200JSONResponse{Template: tpl}, nil
+}
+
+// CheckWriteTemplate реализует gen.StrictServerInterface.
+func (h *Handler) CheckWriteTemplate(ctx context.Context, req gen.CheckWriteTemplateRequestObject) (gen.CheckWriteTemplateResponseObject, error) {
+	res, err := h.svc.CheckWriteTemplate(ctx, req.Id, req.Body.Template)
+	if err != nil {
+		return nil, err
+	}
+	out := gen.CheckWriteTemplate200JSONResponse{
+		Ok: res.OK, Total: res.Total, RoundTrip: res.RoundTrip, SamePath: res.SamePath,
+		Mismatches: make([]gen.WriteTemplateMismatch, 0, len(res.Mismatches)),
+	}
+	for _, m := range res.Mismatches {
+		dto := gen.WriteTemplateMismatch{RelPath: m.RelPath, Fields: m.Fields}
+		if dto.Fields == nil {
+			dto.Fields = []string{}
+		}
+		if m.Rendered != "" {
+			dto.Rendered = &m.Rendered
+		}
+		if m.Error != "" {
+			dto.Error = &m.Error
+		}
+		out.Mismatches = append(out.Mismatches, dto)
+	}
+	return out, nil
 }
 
 func patternsDTO(rows []PatternRow) gen.PatternList {