fix: replace all non-ASCII characters with safe ASCII equivalents

Replace box-drawing characters (U+2500) in session log with ASCII dashes.
Replace em dashes (U+2014) in CLAUDE.md template with double hyphens.
Remove em dash from comment in run.go.
Add ASCII-guard tests for session log output and seed templates.
Prevents mojibake on Windows terminals that misinterpret UTF-8 as CP1252.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/session/log.go

@@ -40,7 +40,7 @@ func FormatSessionEntry(info *SessionInfo) string {
 	duration := info.EndTime.Sub(info.StartTime)
 	timeFmt := "2006-01-02 15:04:05"
 
-	fmt.Fprintf(&b, "── Session %s ──\n", info.StartTime.Format(timeFmt))
+	fmt.Fprintf(&b, "-- Session %s --\n", info.StartTime.Format(timeFmt))
 	fmt.Fprintf(&b, "Agent:    %s\n", info.Agent)
 	fmt.Fprintf(&b, "Mode:     %s\n", info.Mode)
 	fmt.Fprintf(&b, "Start:    %s\n", info.StartTime.Format(timeFmt))
@@ -96,7 +96,7 @@ func FormatSessionEntry(info *SessionInfo) string {
 		b.WriteString("(No changes detected)\n")
 	}
 
-	b.WriteString("────────────────────────────────\n")
+	b.WriteString("--------------------------------\n")
 
 	return b.String()
 }