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/platform/config/config.go

@@ -31,6 +31,14 @@ type API struct {
 
 	BootstrapAdminUsername string `env:"BOOTSTRAP_ADMIN_USERNAME" envDefault:"admin"`
 	BootstrapAdminPassword string `env:"BOOTSTRAP_ADMIN_PASSWORD"`
+
+	// LibraryRoot — точки монтирования NFS-хранилищ (общий каталог с storage-agent).
+	LibraryRoot string `env:"LIBRARY_ROOT" envDefault:"/library"`
+	// LibraryHostRoot — LIBRARY_HOST внутри контейнера: local-хранилища — его подпапки.
+	LibraryHostRoot string `env:"LIBRARY_HOST_ROOT" envDefault:"/library-host"`
+	StorageAgentURL string `env:"STORAGE_AGENT_URL" envDefault:"http://storage-agent:8090"`
+	InternalToken   string `env:"INTERNAL_TOKEN"`
+	FFprobePath     string `env:"FFPROBE_PATH" envDefault:"ffprobe"`
 }
 
 // StorageAgent — конфигурация внутреннего сервиса storage-agent.