[Avante.nvim] Add direct support for Cursor through ACP

### Feature request You can do it today with a custom provider: ``` "yetone/avante.nvim", event = "VeryLazy", version = false, build = "make", opts = { debug = false, provider = "cursor", mode = "agentic", acp_providers = { cursor = { command = "/Users/lrobinson/.local/bin/agent", args = { "acp" }, auth_method = "cursor_login", env = { HOME = os.getenv("HOME"), PATH = os.getenv("PATH"), }, }, }, }, ``` But could be cool to make it built-in 😄 ### Motivation Cursor now supports ACP! Can use Composer models, codebase indexing, and more with any editor. ### Other _No response_