feat(api): library sources, scanner and catalog (M2)

- schema for sources, path patterns, media files, artists, albums,
  tracks, genres (migration 00003)
- path patterns (RE2 with named groups, skip), merge with tags by
  source priority, fallbacks from the file name and folder, name
  normalization and multi-artist split
- scanner: walk, skip unchanged files by size and mtime, ffprobe in 8
  workers with a single catalog writer, renames by content hash keep
  the track, duplicates fold into one track with the best file as
  primary, missing files are kept 30 days
- storage-agent mounts NFS with validated server, export and an option
  whitelist, no shell; test mount counts audio files
- admin API: sources CRUD, connection test, patterns with preview,
  scan, library status, file errors, host folder picker; scheduled
  scans and health checks; mounts are restored on start
- catalog API: artist, artist albums, album with tracks, track
- api image is alpine with ffmpeg for ffprobe

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

services/api/internal/library/agent.go

@@ -0,0 +1,105 @@
+package library
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/google/uuid"
+
+	"pipu/api/internal/storageagent"
+)
+
+// Agent — клиент storage-agent (монтирование NFS).
+type Agent interface {
+	Mount(ctx context.Context, sourceID uuid.UUID, spec storageagent.NFSSpec) (storageagent.MountResult, error)
+	Unmount(ctx context.Context, sourceID uuid.UUID) error
+	Test(ctx context.Context, spec storageagent.NFSSpec) (storageagent.MountResult, error)
+}
+
+// HTTPAgent ходит в storage-agent по внутренней сети с общим секретом.
+type HTTPAgent struct {
+	BaseURL string
+	Token   string
+	Client  *http.Client
+}
+
+// NewHTTPAgent создаёт клиента агента.
+func NewHTTPAgent(baseURL, token string) *HTTPAgent {
+	return &HTTPAgent{BaseURL: baseURL, Token: token, Client: &http.Client{Timeout: 40 * time.Second}}
+}
+
+// AgentError — агент отклонил запрос (например, недопустимые параметры NFS).
+type AgentError struct {
+	Status int
+	Field  string
+	Reason string
+}
+
+func (e *AgentError) Error() string {
+	return fmt.Sprintf("storage-agent: %d %s %s", e.Status, e.Field, e.Reason)
+}
+
+func (a *HTTPAgent) do(ctx context.Context, method, path string, body any, out any) error {
+	var rd *bytes.Reader
+	if body != nil {
+		raw, err := json.Marshal(body)
+		if err != nil {
+			return err
+		}
+		rd = bytes.NewReader(raw)
+	} else {
+		rd = bytes.NewReader(nil)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, a.BaseURL+path, rd)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Authorization", "Bearer "+a.Token)
+	req.Header.Set("Content-Type", "application/json")
+	res, err := a.Client.Do(req)
+	if err != nil {
+		return fmt.Errorf("storage-agent: %w", err)
+	}
+	defer func() { _ = res.Body.Close() }()
+	if res.StatusCode >= 400 {
+		var p struct {
+			Detail string `json:"detail"`
+			Errors []struct {
+				Field string `json:"field"`
+			} `json:"errors"`
+		}
+		_ = json.NewDecoder(res.Body).Decode(&p)
+		ae := &AgentError{Status: res.StatusCode, Reason: p.Detail}
+		if len(p.Errors) > 0 {
+			ae.Field = p.Errors[0].Field
+		}
+		return ae
+	}
+	if out != nil {
+		return json.NewDecoder(res.Body).Decode(out)
+	}
+	return nil
+}
+
+// Mount реализует Agent.
+func (a *HTTPAgent) Mount(ctx context.Context, id uuid.UUID, spec storageagent.NFSSpec) (storageagent.MountResult, error) {
+	var res storageagent.MountResult
+	err := a.do(ctx, http.MethodPost, "/internal/mounts", storageagent.MountRequest{SourceID: id.String(), NFSSpec: spec}, &res)
+	return res, err
+}
+
+// Unmount реализует Agent.
+func (a *HTTPAgent) Unmount(ctx context.Context, id uuid.UUID) error {
+	return a.do(ctx, http.MethodDelete, "/internal/mounts/"+id.String(), nil, nil)
+}
+
+// Test реализует Agent.
+func (a *HTTPAgent) Test(ctx context.Context, spec storageagent.NFSSpec) (storageagent.MountResult, error) {
+	var res storageagent.MountResult
+	err := a.do(ctx, http.MethodPost, "/internal/mounts/test", spec, &res)
+	return res, err
+}