sync: update CLI for Beginners learning hub (2026-05-08)

- 00-quick-start: add Optional shell tab completion details section
  (copilot completion bash|zsh|fish commands, persistent setup)
- 04-agents-and-custom-instructions: remove mention that /init generates
  AGENTS.md; keep 'write your own' guidance instead
- Bump lastUpdated to 2026-05-08 for both pages

Upstream commits synced:
- 0ddfebd: docs: update course content with Copilot CLI v1.0.37-v1.0.40 features
- af9965758d61: Refine Copilot CLI course updates
- fbf8db99: Merge PR #109 (remove /init AGENTS.md generation mention)
- 54b2b645: Merge PR #87 (fix formatting in 01-setup-and-first-steps)
- 7c7acb1d: latest SHA

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

website/src/content/docs/learning-hub/cli-for-beginners/00-quick-start.md

@@ -3,7 +3,7 @@ title: '00 · Quick Start'
 description: 'Install GitHub Copilot CLI, authenticate, and verify your environment with the same flow as the source course.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-03-20
+lastUpdated: 2026-05-08
 ---
 
 ![Chapter 00: Quick Start](/images/learning-hub/copilot-cli-for-beginners/00/chapter-header.png)
@@ -90,6 +90,31 @@ winget install GitHub.Copilot
 curl -fsSL https://gh.io/copilot-install | bash
 ```
 
+<details>
+<summary>Optional: Enable shell tab completion</summary>
+
+Shell tab completion lets you press **Tab** to complete `copilot` subcommands, command options, and some option values. This is optional, but it can be handy once you're comfortable using the CLI.
+
+Copilot CLI currently supports completion scripts for Bash, Zsh, and Fish:
+
+```shell
+# Bash, current session only
+source <(copilot completion bash)
+
+# Bash, persistent on Linux
+copilot completion bash | sudo tee /etc/bash_completion.d/copilot
+
+# Zsh
+copilot completion zsh > "${fpath[1]}/_copilot"
+
+# Fish
+copilot completion fish > ~/.config/fish/completions/copilot.fish
+```
+
+Restart your shell after adding persistent completion. PowerShell is supported for running Copilot CLI on Windows, but `copilot completion` currently supports only Bash, Zsh, and Fish.
+
+</details>
+
 ---
 
 ## Authentication

website/src/content/docs/learning-hub/cli-for-beginners/04-agents-and-custom-instructions.md

@@ -3,7 +3,7 @@ title: '04 · Create Specialized AI Assistants'
 description: 'Mirror the source chapter on custom agents and custom instructions for GitHub Copilot CLI.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-03-20
+lastUpdated: 2026-05-08
 ---
 
 ![Chapter 04: Agents and Custom Instructions](/images/learning-hub/copilot-cli-for-beginners/04/chapter-header.png)
@@ -438,7 +438,7 @@ Copilot will scan your project and create tailored instruction files. You can ed
 
 `AGENTS.md` is the recommended format. It's an [open standard](https://agents.md/) that works across Copilot and other AI coding tools. Place it in your repository root and Copilot reads it automatically. This project's own [AGENTS.md](https://github.com/github/copilot-cli-for-beginners/blob/main/AGENTS.md) is a working example.
 
-A typical `AGENTS.md` describes your project context, code style, security requirements, and testing standards. Use `/init` to generate one, or write your own following the pattern in our example file.
+A typical `AGENTS.md` describes your project context, code style, security requirements, and testing standards. Write your own following the pattern in our example file.
 
 ### Custom Instruction Files (.instructions.md)