docs(shell-docs): make skills install one-shot with -g -y

The build-with-agents guide recommended a bare `npx skills add` that drops
human users into a multi-step interactive flow (skill multiselect, agent
selection, scope, install method, confirm). Recommend `-g -y` so all skills
install globally in one shot, with a Callout pointing to the flag-less command
for users who want to choose interactively.

Author: onsclom

showcase/shell-docs/src/content/snippets/shared/guides/build-with-agents.mdx

@@ -15,10 +15,14 @@ Skills are folders of instructions, references, and scripts that coding agents c
     Run the following command to install CopilotKit skills into your agent environment:
 
     ```bash
-    npx skills add CopilotKit/CopilotKit
+    npx skills add CopilotKit/CopilotKit -g -y
     ```
 
-    This pulls the latest skills directly from the CopilotKit repository and installs them into your tool's skills directory (e.g. `~/.claude/skills/` for Claude Code). The CopilotKit MCP server is also auto-wired so your agent has live documentation access.
+    The `-g -y` flags install **every** CopilotKit skill globally without prompting you to pick them one by one. This pulls the latest skills directly from the CopilotKit repository into your tool's global skills directory (e.g. `~/.claude/skills/` for Claude Code), so they're available across all your projects. The CopilotKit MCP server is also auto-wired so your agent has live documentation access.
+
+    <Callout type="info">
+      Want to choose what gets installed? Run `npx skills add CopilotKit/CopilotKit` without the flags to pick specific skills, target agents, and scope interactively.
+    </Callout>
 
     Skills cover project setup, building AI features, connecting agent frameworks, debugging, and version upgrades. The full list is in the [CopilotKit skills directory](https://github.com/CopilotKit/CopilotKit/tree/main/skills).