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/SearchInventoryTool.php

@@ -11,6 +11,7 @@ use App\Repository\PieceRepository;
 use App\Repository\ProductRepository;
 use App\Repository\SiteRepository;
 use Mcp\Capability\Attribute\McpTool;
+use Mcp\Schema\Result\CallToolResult;
 
 #[McpTool(
     name: 'search_inventory',
@@ -31,7 +32,7 @@ class SearchInventoryTool
         private readonly ConstructeurRepository $constructeurs,
     ) {}
 
-    public function __invoke(string $query, string $types = '', int $limit = 20): array
+    public function __invoke(string $query, string $types = '', int $limit = 20): CallToolResult
     {
         $query = trim($query);
         if ('' === $query) {