chore: name skills@latest in the agent setup install command

.changeset/agent-setup-npx-skills-latest.md

@@ -0,0 +1,5 @@
+---
+"slack": patch
+---
+
+Name `skills@latest` in the agent setup prompt's `npx skills` install command, so tracking the latest `skills` release reads as a deliberate choice. Current npm already resolves the latest release for a bare `npx skills`, so the installed version does not change.

public/agent-setup/prompt.md

@@ -87,7 +87,7 @@ The plugin loads in the user's next Codex session. Do not ask the user to restar
 Install the Slack skills with [`npx skills`](https://github.com/vercel-labs/skills#supported-agents), passing your own agent identifier to `-a`:
 
 ```sh
-npx -y skills add slackapi/slack-skills-plugin -g -y -a <agent>
+npx -y skills@latest add slackapi/slack-skills-plugin -g -y -a <agent>
 ```
 
 The `-g` flag installs the skills for the user rather than the current folder, so they are available in the new app's folder and every later session. If the skills are already installed, the same command replaces them with the latest version. For example, `-a cursor` for Cursor, `-a gemini-cli` for Gemini CLI, or `-a opencode` for OpenCode. See the [supported agents list](https://github.com/vercel-labs/skills#supported-agents) for every identifier.

tests/unit/test_agent_setup_prompt.py

@@ -9,7 +9,7 @@
 SHELL_TO_README = (
     ("claude plugin install ", "/plugin install "),
     ("claude plugin marketplace add ", "/plugin marketplace add "),
-    ("npx -y skills ", "npx skills "),
+    ("npx -y skills@latest ", "npx skills "),
     (" -g ", " "),
 )