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-app/src/main/java/com/cameleer3/server/app/controller/DetailController.java

@@ -0,0 +1,54 @@
+package com.cameleer3.server.app.controller;
+
+import com.cameleer3.server.app.storage.ClickHouseExecutionRepository;
+import com.cameleer3.server.core.detail.DetailService;
+import com.cameleer3.server.core.detail.ExecutionDetail;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.tags.Tag;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Map;
+
+/**
+ * Endpoints for retrieving execution details and processor snapshots.
+ * <p>
+ * The detail endpoint returns a nested processor tree reconstructed from
+ * flat parallel arrays stored in ClickHouse. The snapshot endpoint returns
+ * per-processor exchange data (bodies and headers).
+ */
+@RestController
+@RequestMapping("/api/v1/executions")
+@Tag(name = "Detail", description = "Execution detail and processor snapshot endpoints")
+public class DetailController {
+
+    private final DetailService detailService;
+    private final ClickHouseExecutionRepository executionRepository;
+
+    public DetailController(DetailService detailService,
+                            ClickHouseExecutionRepository executionRepository) {
+        this.detailService = detailService;
+        this.executionRepository = executionRepository;
+    }
+
+    @GetMapping("/{executionId}")
+    @Operation(summary = "Get execution detail with nested processor tree")
+    public ResponseEntity<ExecutionDetail> getDetail(@PathVariable String executionId) {
+        return detailService.getDetail(executionId)
+                .map(ResponseEntity::ok)
+                .orElse(ResponseEntity.notFound().build());
+    }
+
+    @GetMapping("/{executionId}/processors/{index}/snapshot")
+    @Operation(summary = "Get exchange snapshot for a specific processor")
+    public ResponseEntity<Map<String, String>> getProcessorSnapshot(
+            @PathVariable String executionId,
+            @PathVariable int index) {
+        return executionRepository.findProcessorSnapshot(executionId, index)
+                .map(ResponseEntity::ok)
+                .orElse(ResponseEntity.notFound().build());
+    }
+}