Per-agent x64dbg session through debugger()/debugger_tools()

Harbor starts the x64dbg-automate MCP server (stdio) on first use and keeps
it for the life of the agent's Harbor process; the debuggee is terminated
when that process exits. Configured by debugger_command/_path/_temp in
[reverse].

tests/fake_stdio_mcp.py

@@ -0,0 +1,18 @@
+"""A fake stdio MCP server for the debugger forwarder test: one tool that echoes, one that fails."""
+import json
+import sys
+
+for line in sys.stdin:
+    msg = json.loads(line)
+    if "id" not in msg:
+        continue
+    if msg["method"] == "initialize":
+        result = {"protocolVersion": "2025-06-18"}
+    elif msg["method"] == "tools/list":
+        result = {"tools": [{"name": "echo", "description": "Echo", "inputSchema": {"properties": {"x": {}}}}]}
+    elif msg["params"]["name"] == "echo":
+        result = {"content": [{"type": "text", "text": "echo " + json.dumps(msg["params"]["arguments"])}]}
+    else:
+        result = {"isError": True, "content": [{"type": "text", "text": "no such session"}]}
+    print(json.dumps({"jsonrpc": "2.0", "method": "notifications/message", "params": {}}), flush=True)
+    print(json.dumps({"jsonrpc": "2.0", "id": msg["id"], "result": result}), flush=True)