add: show metadata, streams, and clock-time ETA in status UI

Surface the fetched job metadata (show/episode or movie title, season,
episode, release/airdate, media type) and the source audio/subtitle streams
through the tracker and /status, and render them in the dashboard's current-job
card. Audio channel counts are now probed and shown as 5.1/2.0/etc.

ETA now reads as a wall-clock finish time plus remaining duration, e.g.
"17:49 (3h52m)". Recent events drop the per-row date for a WhatsApp-style
Today/Yesterday/date divider with time-only rows. All dynamic strings are
HTML-escaped, since metadata and filenames are user-controlled.

internal/encoder/encoder.go

@@ -45,6 +45,7 @@ type StreamMetadata struct {
 	Index     int    `json:"index"`
 	CodecType string `json:"codec_type"`
 	CodecName string `json:"codec_name"`
+	Channels  int    `json:"channels"`
 	Language  string `json:"tags"`
 	Title     string `json:"title"`
 }
@@ -177,6 +178,7 @@ func (e *Encoder) GetStreamLanguages(ctx context.Context, path string) ([]Stream
 			Index     int               `json:"index"`
 			CodecType string            `json:"codec_type"`
 			CodecName string            `json:"codec_name"`
+			Channels  int               `json:"channels"`
 			Tags      map[string]string `json:"tags"`
 		} `json:"streams"`
 	}
@@ -196,6 +198,7 @@ func (e *Encoder) GetStreamLanguages(ctx context.Context, path string) ([]Stream
 			Index:     s.Index,
 			CodecType: s.CodecType,
 			CodecName: s.CodecName,
+			Channels:  s.Channels,
 			Language:  lang,
 			Title:     title,
 		})