feat(01-03): implement exit summary and verbose window output formatting

- Add PrintSummary writing per-protocol packet counts with percentages and TOTAL to io.Writer
- Add PrintWindowLine writing single verbose window activity line in [window N] CLASS:count format
- Add AccumulateTotals merging WindowSnapshot counts into cumulative totals map
- Output sorted alphabetically for deterministic display
- Add 6 tests: PrintSummary, PrintSummaryEmpty, PrintSummarySorted, PrintWindowLine, PrintWindowLineEmpty, AccumulateTotals

aggregate/summary.go

@@ -0,0 +1,69 @@
+package aggregate
+
+import (
+	"fmt"
+	"io"
+	"sort"
+
+	"github.com/netsynth/netsynth/classify"
+)
+
+// PrintSummary writes a per-protocol packet count summary to w (typically os.Stderr).
+// Output format matches tcpdump conventions (CLAS-03): per-protocol counts with
+// percentages and a TOTAL line, sorted alphabetically for stable output.
+func PrintSummary(w io.Writer, totals map[classify.TrafficClass]int64) {
+	var totalPackets int64
+	for _, count := range totals {
+		totalPackets += count
+	}
+
+	fmt.Fprintln(w, "\n--- Protocol Summary ---")
+
+	// Sort classes for stable output.
+	classes := make([]string, 0, len(totals))
+	for c := range totals {
+		classes = append(classes, string(c))
+	}
+	sort.Strings(classes)
+
+	for _, className := range classes {
+		c := classify.TrafficClass(className)
+		count := totals[c]
+		pct := 0.0
+		if totalPackets > 0 {
+			pct = float64(count) / float64(totalPackets) * 100.0
+		}
+		fmt.Fprintf(w, "  %-15s %8d packets (%5.1f%%)\n", c, count, pct)
+	}
+	fmt.Fprintf(w, "  %-15s %8d packets\n", "TOTAL", totalPackets)
+}
+
+// PrintWindowLine writes a single verbose per-window activity line to w (CLAS-04).
+// Format: [window N] CLASS:count CLASS:count ... (total: N)
+// Classes with zero counts are omitted. Output is sorted for deterministic display.
+func PrintWindowLine(w io.Writer, snap classify.WindowSnapshot) {
+	fmt.Fprintf(w, "[window %d]", snap.WindowIndex)
+
+	// Sort for stable output.
+	classes := make([]string, 0, len(snap.Counts))
+	for c := range snap.Counts {
+		classes = append(classes, string(c))
+	}
+	sort.Strings(classes)
+
+	for _, className := range classes {
+		c := classify.TrafficClass(className)
+		if snap.Counts[c] > 0 {
+			fmt.Fprintf(w, " %s:%d", c, snap.Counts[c])
+		}
+	}
+	fmt.Fprintf(w, " (total: %d)\n", snap.TotalPackets)
+}
+
+// AccumulateTotals merges a WindowSnapshot's counts into cumulative totals.
+// This is used to build the final summary passed to PrintSummary.
+func AccumulateTotals(totals map[classify.TrafficClass]int64, snap classify.WindowSnapshot) {
+	for class, count := range snap.Counts {
+		totals[class] += count
+	}
+}