feat: add mycursor backend; drop myagents xiaohe entrypoint

Cursor Agent CLI wrapper (mycursor) with resume/session listing.
Product xiaohe CLI stays in xiaohe-api only — no dual entry.

Makefile

@@ -1,7 +1,7 @@
 ROOT_DIR := $(shell pwd)
 VENV_BIN_DIR := $(ROOT_DIR)/.venv/bin
 USER_BIN_DIR := $(HOME)/.local/bin
-COMMANDS := myagents myclaude mykimi mycodex myhermes
+COMMANDS := myagents myclaude mykimi mycodex myhermes mycursor
 
 .PHONY: help install uninstall _symlink-commands