ci: add explicit e2e tests step to PR validation

Split test run into unit tests and e2e tests for better visibility
and clearer CI output.

Author: mattapperson

.github/actions/validate-sdk/action.yaml

@@ -47,8 +47,14 @@ runs:
       working-directory: examples/nextjs-example
       run: npx tsc --noEmit
 
-    - name: Run tests
+    - name: Run unit tests
       shell: bash
       env:
         OPENROUTER_API_KEY: ${{ inputs.openrouter-api-key }}
-      run: npx vitest --run
+      run: npx vitest --run --exclude 'tests/e2e/**'
+
+    - name: Run e2e tests
+      shell: bash
+      env:
+        OPENROUTER_API_KEY: ${{ inputs.openrouter-api-key }}
+      run: npx vitest --run tests/e2e/