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/service_test.go

@@ -0,0 +1,33 @@
+package pgmonitor
+
+import "testing"
+
+func TestClampLimit(t *testing.T) {
+	if clampLimit(0, 20, 100) != 20 {
+		t.Fatal("default")
+	}
+	if clampLimit(200, 20, 100) != 100 {
+		t.Fatal("max")
+	}
+	if clampLimit(5, 20, 100) != 5 {
+		t.Fatal("value")
+	}
+}
+
+func TestIsSafeIdent(t *testing.T) {
+	if !isSafeIdent("revision_materialized_prefix") {
+		t.Fatal("valid")
+	}
+	if isSafeIdent("bad-name") {
+		t.Fatal("invalid")
+	}
+	if !isSafeIdent("") {
+		t.Fatal("empty ok")
+	}
+}
+
+func TestNewServiceNilPool(t *testing.T) {
+	if NewService(nil) != nil {
+		t.Fatal("expected nil service")
+	}
+}