Add per-disk profiles with video transcoding support

Each disk stores .jukebox/profile.json with copy parameters (dest
folder, overwrite mode, file select, reserve space, auto-copy) and
optional transcoding limits for the target player (codec, resolution,
bitrate, FPS, audio channels, output format).

On copy, video files are probed with ffprobe; if they exceed the
profile limits they are transcoded via ffmpeg (-threads 0 for full
CPU usage), otherwise copied as-is. Scale filter never upscales.

New: internal/disk/profile.go, internal/transcoder/{detect,transcoder}.go
API: GET/PUT /api/disks/profile?mount_path=
UI: disk profile panel in dashboard for known disks
Dockerfile: adds ffmpeg to the runtime image

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/disk/profile.go

@@ -0,0 +1,70 @@
+package disk
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+type DiskProfile struct {
+	DestFolder     string  `json:"dest_folder"`
+	OverwriteMode  string  `json:"overwrite_mode"`
+	FileSelectMode string  `json:"file_select_mode"`
+	ReserveFreeGB  float64 `json:"reserve_free_gb"`
+	AutoCopy       bool    `json:"auto_copy"`
+
+	// nil = не транскодировать видео
+	Transcode *TranscodeProfile `json:"transcode,omitempty"`
+}
+
+type TranscodeProfile struct {
+	VideoCodec       string `json:"video_codec"`        // "h264" | "h265" | "mpeg4"
+	MaxResolution    string `json:"max_resolution"`     // "480p" | "720p" | "1080p"
+	MaxVideoBitrate  string `json:"max_video_bitrate"`  // "1000k" | "2000k" | "" (без лимита)
+	MaxFPS           int    `json:"max_fps"`            // 0=без лимита | 24 | 25 | 30
+	AudioCodec       string `json:"audio_codec"`        // "aac" | "mp3"
+	MaxAudioBitrate  string `json:"max_audio_bitrate"`  // "128k" | "192k" | ""
+	MaxAudioChannels int    `json:"max_audio_channels"` // 2=стерео | 6=5.1
+	OutputFormat     string `json:"output_format"`      // "mp4" | "mkv" | "avi"
+}
+
+const profileFile = "profile.json"
+
+func profilePath(mountPath string) string {
+	return filepath.Join(mountPath, MarkerDir, profileFile)
+}
+
+func LoadProfile(mountPath string) (*DiskProfile, error) {
+	data, err := os.ReadFile(profilePath(mountPath))
+	if err != nil {
+		return nil, err
+	}
+	var p DiskProfile
+	if err := json.Unmarshal(data, &p); err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+func SaveProfile(mountPath string, p *DiskProfile) error {
+	data, err := json.MarshalIndent(p, "", "  ")
+	if err != nil {
+		return err
+	}
+	path := profilePath(mountPath)
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, data, 0o644); err != nil {
+		return err
+	}
+	return os.Rename(tmp, path)
+}
+
+func DefaultProfile() *DiskProfile {
+	return &DiskProfile{
+		DestFolder:     "media",
+		OverwriteMode:  "skip",
+		FileSelectMode: "new",
+		ReserveFreeGB:  2.0,
+		AutoCopy:       false,
+	}
+}