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/commands/runtime.go

@@ -31,6 +31,7 @@ type MCPToolInfo struct {
 type ContextStats struct {
 	UsedTokens        int
 	TotalTokens       int // model context window
+	HistoryTokens     int // history-only tokens (what maybeSummarize checks)
 	CompressAtTokens  int // hard budget compression threshold
 	SummarizeAtTokens int // soft summarization trigger
 	UsedPercent       int // 0-100