fix(ci): add dedicated CI test workflow

Adds .github/workflows/ci.yml so PRs touching Go code are validated
independently of the release workflow. Previously the test job was
co-located inside release.yml gated on `startsWith(github.ref, 'refs/tags/v')`,
meaning no automated test ran on PRs until a tag was pushed.

The new workflow mirrors the release.yml test job (go mod tidy, go vet, go test
-race) and triggers on every push to main and every pull request that touches
Go code, using Go 1.25 to match release.yml.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,39 @@
+name: CI / Test
+
+# Runs on every PR touching Go code, and on every push to main.
+# Mirrors the test job from release.yml so PRs are validated independently
+# of the release workflow. Uses Go 1.25 to match release.yml.
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - '**.go'
+      - 'go.mod'
+      - 'go.sum'
+      - '.github/workflows/ci.yml'
+  pull_request:
+    paths:
+      - '**.go'
+      - 'go.mod'
+      - 'go.sum'
+      - '.github/workflows/ci.yml'
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: '1.25'
+          cache: true
+      - name: Tidy
+        run: go mod tidy && git diff --exit-code go.sum
+      - name: Vet
+        run: go vet ./...
+      - name: Test
+        run: go test -race -count=1 ./...