fix: show first progress update immediately instead of waiting for 5%

- Always show the first nonzero progress update so users don't see 0% for
  extended periods on slow downloads or fragment-based downloads
- Keep 5% throttle for subsequent updates to avoid excessive API calls
- Add readProgress summary logging (lines, matches, stderr length)
- Fix progressKeyboard not being updated until progress >= 5%

internal/dl/progress.go

@@ -3,6 +3,7 @@ package dl
 import (
 	"bufio"
 	"io"
+	"log/slog"
 	"regexp"
 	"strconv"
 	"strings"
@@ -60,8 +61,11 @@ func parseProgressLine(line string) *progressUpdate {
 func readProgress(stderr io.ReadCloser, updates chan<- *domain.DownloadJob, job *domain.DownloadJob) {
 	var stderrBuf strings.Builder
 	scanner := bufio.NewScanner(stderr)
+	lineCount := 0
+	matchCount := 0
 	for scanner.Scan() {
 		line := scanner.Text()
+		lineCount++
 
 		if stderrBuf.Len() < 4096 {
 			stderrBuf.WriteString(line)
@@ -72,10 +76,12 @@ func readProgress(stderr io.ReadCloser, updates chan<- *domain.DownloadJob, job
 		if parsed == nil {
 			continue
 		}
+		matchCount++
 		job.Progress = parsed.pct
 		job.Speed = parsed.speed
 		job.ETA = parsed.eta
 		updates <- job
 	}
 	job.StderrLog = stderrBuf.String()
+	slog.Info("readProgress finished", "url", job.URL, "lines", lineCount, "matches", matchCount, "stderr_len", len(job.StderrLog))
 }