Fix CI workflow for integration tests

- Remove unused services block that caused CI failure
  (Gitea runner doesn't support --name/-p in options field)
- Update build tag to modern //go:build syntax (Go 1.17+)

The workflow already manually installs and starts NATS with JetStream,
making the services block redundant.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -20,12 +20,6 @@ jobs:
 
   integration:
     runs-on: ubuntu-latest
-    services:
-      nats:
-        image: nats:latest
-        options: --name nats -p 4222:4222
-        # Enable JetStream via command line args
-        # Note: The 'args' field may not be supported in all CI runners
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5

store/jetstream_integration_test.go

@@ -1,4 +1,4 @@
-// +build integration
+//go:build integration
 
 package store