fix(context): expose history tokens and remove leaked state files

Address remaining review feedback: 1) Add HistoryTokens field to ContextUsage/ContextStats, showing history-only token count in /context and frontend UI alongside SummarizeAtTokens so users can see the actual summarization trigger comparison. 2) Remove .codebuddy/github-contribute/ state files accidentally included in the PR.

pkg/channels/pico/pico.go

@@ -1396,6 +1396,7 @@ func setContextUsagePayload(payload map[string]any, u *bus.ContextUsage) {
 	payload["context_usage"] = map[string]any{
 		"used_tokens":         u.UsedTokens,
 		"total_tokens":        u.TotalTokens,
+		"history_tokens":      u.HistoryTokens,
 		"compress_at_tokens":  u.CompressAtTokens,
 		"summarize_at_tokens": u.SummarizeAtTokens,
 		"used_percent":        u.UsedPercent,

pkg/channels/pico/pico_test.go

@@ -604,6 +604,7 @@ func TestBeginStream_FinalizeIncludesContextUsage(t *testing.T) {
 	if err := contextStreamer.FinalizeWithContext(context.Background(), "final", &bus.ContextUsage{
 		UsedTokens:        10,
 		TotalTokens:       100,
+		HistoryTokens:     5,
 		CompressAtTokens:  80,
 		SummarizeAtTokens: 60,
 		UsedPercent:       10,
@@ -628,6 +629,9 @@ func TestBeginStream_FinalizeIncludesContextUsage(t *testing.T) {
 	if got := rawUsage["used_tokens"]; got != float64(10) {
 		t.Fatalf("used_tokens = %#v, want 10", got)
 	}
+	if got := rawUsage["history_tokens"]; got != float64(5) {
+		t.Fatalf("history_tokens = %#v, want 5", got)
+	}
 	if got := rawUsage["summarize_at_tokens"]; got != float64(60) {
 		t.Fatalf("summarize_at_tokens = %#v, want 60", got)
 	}