Add status page enhancements with new metrics and footer

- Add GC statistics (run count, total/last pause, heap usage)
- Add BGP peer count tracking from RIS Live OPEN/NOTIFICATION messages
- Add route churn rate metric (announcements + withdrawals per second)
- Add announcement and withdrawal counters
- Add footer with attribution, license, and git revision
- Embed git revision at build time via ldflags
- Update HTML template to display all new metrics

internal/routewatch/prefixhandler.go

@@ -113,6 +113,10 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 				timestamp:   timestamp,
 				path:        msg.Path,
 			})
+			// Record announcement in metrics
+			if h.metrics != nil {
+				h.metrics.RecordAnnouncement()
+			}
 		}
 	}
 
@@ -126,6 +130,10 @@ func (h *PrefixHandler) HandleMessage(msg *ristypes.RISMessage) {
 			timestamp:   timestamp,
 			path:        msg.Path,
 		})
+		// Record withdrawal in metrics
+		if h.metrics != nil {
+			h.metrics.RecordWithdrawal()
+		}
 	}
 
 	// Check if we need to flush