Serve /api/v1/stats counts from realtime in-memory counters (closes #27)

The stats endpoints recomputed every count with a COUNT(*) over each
table plus a MIN/MAX union scan on every request, which took the whole
timeout and returned 500 once the database passed a few GiB.

The row counts (ASNs, prefixes, peerings, peers, live routes) now live
in memory: seeded once at startup and adjusted on each write as routes
and records are inserted, updated and removed, so a read serves them
with no scan and no timer. A live-route upsert is an UPDATE, then an
INSERT only when no row matched, so its rows-affected count tells a new
route from a re-announced one. Oldest/newest timestamps read one row
from each end of the last_updated index, which also fixes the per-call
scan warning. The distinct-prefix histogram stays a single indexed
query.

JSON shape of /api/v1/stats and the status page is unchanged.

Model: opus-4-8

internal/server/handlers.go

@@ -219,13 +219,6 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 
 		const bitsPerMegabit = 1000000.0
 
-		// Get route counts from database
-		ipv4Routes, ipv6Routes, err := s.db.GetLiveRouteCountsContext(ctx)
-		if err != nil {
-			s.logger.Warn("Failed to get live route counts", "error", err)
-			// Continue with zero counts
-		}
-
 		// Get route update metrics
 		routeMetrics := s.streamer.GetMetricsTracker().GetRouteMetrics()
 
@@ -259,8 +252,8 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 			Peers:                  dbStats.Peers,
 			DatabaseSizeBytes:      dbStats.FileSizeBytes,
 			LiveRoutes:             dbStats.LiveRoutes,
-			IPv4Routes:             ipv4Routes,
-			IPv6Routes:             ipv6Routes,
+			IPv4Routes:             dbStats.IPv4Routes,
+			IPv6Routes:             dbStats.IPv6Routes,
 			OldestRoute:            dbStats.OldestRoute,
 			NewestRoute:            dbStats.NewestRoute,
 			IPv4UpdatesPerSec:      routeMetrics.IPv4UpdatesPerSec,
@@ -439,13 +432,6 @@ func (s *Server) handleStats() http.HandlerFunc {
 
 		const bitsPerMegabit = 1000000.0
 
-		// Get route counts from database
-		ipv4Routes, ipv6Routes, err := s.db.GetLiveRouteCountsContext(ctx)
-		if err != nil {
-			s.logger.Warn("Failed to get live route counts", "error", err)
-			// Continue with zero counts
-		}
-
 		// Get route update metrics
 		routeMetrics := s.streamer.GetMetricsTracker().GetRouteMetrics()
 
@@ -537,8 +523,8 @@ func (s *Server) handleStats() http.HandlerFunc {
 			Peers:                  dbStats.Peers,
 			DatabaseSizeBytes:      dbStats.FileSizeBytes,
 			LiveRoutes:             dbStats.LiveRoutes,
-			IPv4Routes:             ipv4Routes,
-			IPv6Routes:             ipv6Routes,
+			IPv4Routes:             dbStats.IPv4Routes,
+			IPv6Routes:             dbStats.IPv6Routes,
 			OldestRoute:            dbStats.OldestRoute,
 			NewestRoute:            dbStats.NewestRoute,
 			IPv4UpdatesPerSec:      routeMetrics.IPv4UpdatesPerSec,