fix(mcp) : return CallToolResult to prevent structuredContent serialization issue

Tools now return CallToolResult directly instead of Content arrays,
preventing the MCP SDK from auto-generating structuredContent as a
JSON array (which Claude Code rejects — expects a JSON object/record).
Also adds Accept header to test helpers and SSE response parsing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Mcp/Tool/Machine/CloneMachineTool.php

@@ -18,6 +18,7 @@ use App\Repository\MachineProductLinkRepository;
 use App\Repository\MachineRepository;
 use Doctrine\ORM\EntityManagerInterface;
 use Mcp\Capability\Attribute\McpTool;
+use Mcp\Schema\Result\CallToolResult;
 use Symfony\Bundle\SecurityBundle\Security;
 
 #[McpTool(
@@ -42,7 +43,7 @@ class CloneMachineTool
         string $name,
         string $siteId,
         string $reference = '',
-    ): array {
+    ): CallToolResult {
         $this->requireRole($this->security, 'ROLE_GESTIONNAIRE');
 
         $source = $this->machineRepository->find($machineId);