feat(02-03): detail controller, tree reconstruction, processor snapshot endpoint

- Implement findRawById and findProcessorSnapshot in ClickHouseExecutionRepository
- DetailController with GET /executions/{id} returning nested processor tree
- GET /executions/{id}/processors/{index}/snapshot for per-processor exchange data
- 5 unit tests for tree reconstruction (linear, branching, multiple roots, empty)
- 6 integration tests for detail endpoint, snapshot, and 404 handling
- Added assertj and mockito test dependencies to core module

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

cameleer3-server-core/pom.xml

@@ -32,5 +32,15 @@
             <artifactId>junit-jupiter</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 </project>