docs: add Cursor to agent skills directory table

Adds Cursor to the list of AI coding agents that support skills in the
MCP Apps build guide, with links to the official Cursor docs and the
correct skill directory paths for macOS/Linux and Windows.

Author: dsp-ant

docs/extensions/apps/build.mdx

@@ -60,6 +60,7 @@ And then copying the skill to the appropriate location for your agent:
 | [Cline](https://cline.bot/blog/cline-3-48-0-skills-and-websearch-make-cline-smarter)                                                                                         | `~/.cline/skills/`             | `%USERPROFILE%\.cline\skills\`        |
 | [Goose](https://block.github.io/goose/docs/guides/context-engineering/using-skills/)                                                                                         | `~/.config/goose/skills/`      | `%USERPROFILE%\.config\goose\skills\` |
 | [Codex](https://developers.openai.com/codex/skills/)                                                                                                                         | `~/.codex/skills/`             | `%USERPROFILE%\.codex\skills\`        |
+| [Cursor](https://cursor.com/docs/context/skills)                                                                                                                             | `~/.cursor/skills/`            | `%USERPROFILE%\.cursor\skills\`       |
 
 <Note>