chore(release): prepare for v0.4.0 (#151)

## [0.4.0] - 2026-06-16

### 🚀 Features

- *(metrics)* Add SubscriptionMetrics OTel observer for subscriptions (#150)

### 🐛 Bug Fixes

- *(deps)* Update opentelemetry-go monorepo (#146)
- *(deps)* Update module github.com/99designs/gqlgen to v0.17.91 (#148)

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---

**Note:** Please use **Squash Merge** when merging this PR.

Reviewed-on: #151
Co-authored-by: Unbound Releaser <releaser@unbound.se>
Co-committed-by: Unbound Releaser <releaser@unbound.se>

.version

@@ -1,3 +1,3 @@
 {
-  "version": "v0.3.1"
+  "version": "v0.4.0"
 }

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 All notable changes to this project will be documented in this file.
 
+## [0.4.0] - 2026-06-16
+
+### 🚀 Features
+
+- *(metrics)* Add SubscriptionMetrics OTel observer for subscriptions (#150)
+
+### 🐛 Bug Fixes
+
+- *(deps)* Update opentelemetry-go monorepo (#146)
+- *(deps)* Update module github.com/99designs/gqlgen to v0.17.91 (#148)
+
 ## [0.3.1] - 2026-05-29
 
 ### 🐛 Bug Fixes