Add backpressure stack for agentic coding quality gates

PostToolUse hooks run after every file edit:
- Backend: ./mvnw compile (Checkstyle Google Style + javac)
- Frontend: vue-tsc --noEmit + oxlint + ESLint

Stop hook runs test suites when source files changed, blocks the
agent on failure and re-engages it to fix the issue. Output is
filtered to [ERROR] lines only for context efficiency.

Static analysis: Checkstyle (validate phase), SpotBugs (verify phase),
ArchUnit (9 hexagonal architecture rules as JUnit tests).

Fail-fast: Surefire skipAfterFailureCount=1, Vitest bail=1.
Test log noise suppressed via logback-test.xml (WARN level),
redirectTestOutputToFile, and trimStackTrace.

Existing Java sources reformatted to Google Style (2-space indent,
import order, Javadoc on public types).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/java/de/fete/FeteApplication.java

@@ -3,10 +3,12 @@ package de.fete;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
+/** Spring Boot entry point for the fete application. */
 @SpringBootApplication
 public class FeteApplication {
 
-    public static void main(String[] args) {
-        SpringApplication.run(FeteApplication.class, args);
-    }
+  /** Starts the application. */
+  public static void main(String[] args) {
+    SpringApplication.run(FeteApplication.class, args);
+  }
 }

backend/src/main/java/de/fete/adapter/in/web/HealthController.java

@@ -1,15 +1,16 @@
 package de.fete.adapter.in.web;
 
 import java.util.Map;
-
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+/** REST endpoint for health checks. */
 @RestController
 public class HealthController {
 
-    @GetMapping("/health")
-    public Map<String, String> health() {
-        return Map.of("status", "ok");
-    }
+  /** Returns a simple health status. */
+  @GetMapping("/health")
+  public Map<String, String> health() {
+    return Map.of("status", "ok");
+  }
 }