feat(db): implement PostgreSQL monitoring and maintenance features

Added PostgreSQL monitoring and maintenance capabilities to the API, including new endpoints for instance-level metrics, maintenance operations, and job scheduling. Updated the HTTP API to support PostgreSQL monitoring routes and integrated a background scheduler for metrics collection. Enhanced the CLI with database commands for maintenance tasks. Updated documentation to reflect these changes.

internal/pgmonitor/scheduler.go

@@ -0,0 +1,59 @@
+package pgmonitor
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// StartScheduler runs periodic PostgreSQL analyzer snapshots until ctx is cancelled.
+func StartScheduler(ctx context.Context, pool *pgxpool.Pool) {
+	if pool == nil {
+		return
+	}
+	go func() {
+		t5 := time.NewTicker(5 * time.Minute)
+		t15 := time.NewTicker(15 * time.Minute)
+		defer t5.Stop()
+		defer t15.Stop()
+		s := NewService(pool)
+		runLight := func() {
+			c, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+			defer cancel()
+			if err := s.RefreshMetricsSnapshot(c); err != nil {
+				log.Printf("pgmonitor: metrics refresh: %v", err)
+			}
+			if err := s.DetectAutovacuumLag(c); err != nil {
+				log.Printf("pgmonitor: autovacuum lag: %v", err)
+			}
+		}
+		runHeavy := func() {
+			c, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+			defer cancel()
+			if err := s.AggregateSlowQueries(c, 30); err != nil {
+				log.Printf("pgmonitor: slow queries: %v", err)
+			}
+			if err := s.EstimateTableBloat(c); err != nil {
+				log.Printf("pgmonitor: bloat: %v", err)
+			}
+			if err := s.AnalyzeIndexUsage(c); err != nil {
+				log.Printf("pgmonitor: index usage: %v", err)
+			}
+		}
+		runLight()
+		runHeavy()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-t5.C:
+				runLight()
+			case <-t15.C:
+				runHeavy()
+			}
+		}
+	}()
+	log.Printf("pgmonitor: scheduler started (5m light / 15m heavy)")
+}