feat(02-04): populate diagram_content_hash during ingestion and fix test stability

- Inject DiagramRepository into ClickHouseExecutionRepository for hash lookup
- Replace empty string placeholder with actual SHA-256 diagram hash in insertBatch
- Add Surefire/Failsafe forkCount=1 reuseForks=false for classloader isolation
- Add failsafe-plugin integration-test/verify goals for IT execution
- Create DiagramLinkingIT with positive (hash populated) and negative (empty fallback) cases
- Fix flaky awaitility assertions with ignoreExceptions for EmptyResultDataAccess
- Increase IngestionSchemaIT timeouts to 30s for reliable batch flush waits
- Adjust SearchControllerIT pagination assertion to match correct seed data count

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

cameleer3-server-app/pom.xml

@@ -90,6 +90,30 @@
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <configuration>
+                    <forkCount>1</forkCount>
+                    <reuseForks>false</reuseForks>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-failsafe-plugin</artifactId>
+                <configuration>
+                    <forkCount>1</forkCount>
+                    <reuseForks>false</reuseForks>
+                </configuration>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>integration-test</goal>
+                            <goal>verify</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
 </project>