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>

.mcp.json

@@ -1,14 +1,12 @@
 {
-  "mcpServers": {
-    "inventory": {
-      "command": "docker",
-      "args": [
-        "exec", "-i",
-        "-e", "MCP_PROFILE_ID=REPLACE_WITH_YOUR_PROFILE_ID",
-        "-e", "MCP_PROFILE_PASSWORD=REPLACE_WITH_YOUR_PASSWORD",
-        "php-inventory-apache",
-        "php", "bin/console", "mcp:server"
-      ]
+    "mcpServers": {
+        "inventory": {
+            "type": "http",
+            "url": "http://inventory.malio-dev.fr/_mcp",
+            "headers": {
+                "X-Profile-Id": "admin-default-profile",
+                "X-Profile-Password": "A123"
+            }
+        }
     }
-  }
 }