Inherit the platform contract tests, and extend the shared Renovate preset

PlatformWebContract asserts what this app must do because it is on the platform: an /api
path matching no controller 404s rather than returning the SPA, health is UP, the liveness
and readiness probes exist, and a client-side route forwards to the shell. That first one
shipped broken to six live sites and was found by typing a URL by hand; now it fails a
build instead.

renovate.json is three lines pointing at austin/renovate-config. The rules were copied per
repo, so they matched only by luck and a change was six edits.

Platform 0.1.9.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XXKjx7FNyRVAjU8dgB5KhN

src/test/java/net/reformedwitness/rwn/PlatformContractTest.java

@@ -0,0 +1,21 @@
+package net.reformedwitness.rwn;
+
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
+import org.testcontainers.containers.PostgreSQLContainer;
+import org.testcontainers.junit.jupiter.Container;
+import org.testcontainers.junit.jupiter.Testcontainers;
+import org.testcontainers.utility.DockerImageName;
+
+import net.thebennett.platform.test.PlatformWebContract;
+
+/** Everything in {@link PlatformWebContract} — what this app must do because it is on the platform. */
+@SpringBootTest
+@Testcontainers
+class PlatformContractTest extends PlatformWebContract {
+
+    @Container
+    @ServiceConnection
+    static PostgreSQLContainer<?> postgres =
+            new PostgreSQLContainer<>(DockerImageName.parse("postgres:18-alpine"));
+}