feat(db): migrate from MySQL to PostgreSQL

Replace MySQL driver with pgx/v5 and pgxpool:
- Update sqlc to use postgresql engine
- Convert query.sql to PostgreSQL syntax ($1 params, CASE WHEN,
  ANY() arrays)
- Replace sql.DB with pgxpool.Pool throughout
- Change nullable types from sql.Null* to pgtype.*
- Update ID types from uint32 to int64 for PostgreSQL compatibility
- Delete MySQL-specific dynamic_connect.go
- Add opentelemetry.gowrap template for tracing

ntpdb/opentelemetry.gowrap

@@ -0,0 +1,55 @@
+import (
+    "context"
+
+    _codes "go.opentelemetry.io/otel/codes"
+    "go.opentelemetry.io/otel"
+    "go.opentelemetry.io/otel/attribute"
+)
+
+{{ $decorator := (or .Vars.DecoratorName (printf "%sWithTracing" .Interface.Name)) }}
+{{ $spanNameType := (or .Vars.SpanNamePrefix .Interface.Name) }}
+
+// {{$decorator}} implements {{.Interface.Name}} interface instrumented with open telemetry spans
+type {{$decorator}} struct {
+  {{.Interface.Type}}
+  _instance string
+  _spanDecorator func(span trace.Span, params, results map[string]interface{})
+}
+
+// New{{$decorator}} returns {{$decorator}}
+func New{{$decorator}} (base {{.Interface.Type}}, instance string, spanDecorator ...func(span trace.Span, params, results map[string]interface{})) {{$decorator}} {
+  d := {{$decorator}} {
+    {{.Interface.Name}}: base,
+    _instance: instance,
+  }
+
+  if len(spanDecorator) > 0 && spanDecorator[0] != nil {
+    d._spanDecorator = spanDecorator[0]
+  }
+
+  return d
+}
+
+{{range $method := .Interface.Methods}}
+  {{if $method.AcceptsContext}}
+    // {{$method.Name}} implements {{$.Interface.Name}}
+func (_d {{$decorator}}) {{$method.Declaration}} {
+  ctx, _span := otel.Tracer(_d._instance).Start(ctx, "{{$spanNameType}}.{{$method.Name}}")
+  defer func() {
+    if _d._spanDecorator != nil {
+      _d._spanDecorator(_span, {{$method.ParamsMap}}, {{$method.ResultsMap}})
+    }{{- if $method.ReturnsError}} else if err != nil {
+      _span.RecordError(err)
+      _span.SetStatus(_codes.Error, err.Error())
+      _span.SetAttributes(
+        attribute.String("event", "error"),
+        attribute.String("message", err.Error()),
+      )
+    }
+    {{end}}
+    _span.End()
+  }()
+  {{$method.Pass (printf "_d.%s." $.Interface.Name) }}
+}
+  {{end}}
+{{end}}