docs: update Learning Hub with recent Copilot CLI features (v1.0.23-v1.0.30) (#1421)

- copilot-configuration-basics.md: Add /ask, /env, /statusline commands
  and --mode/--autopilot/--plan startup flags
- automating-with-hooks.md: Document preToolUse modifiedArgs/updatedInput
  and additionalContext fields for modifying tool arguments
- understanding-mcp-servers.md: Add /mcp install registry section and
  note that type field is optional for remote MCP servers
- installing-and-using-plugins.md: Add copilot plugin marketplace update
  command and deprecation notice for repo/URL/path installs
- using-copilot-coding-agent.md: Add Remote Control section
  (replaces steering feature)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/copilot-configuration-basics.md

@@ -3,7 +3,7 @@ title: 'Copilot Configuration Basics'
 description: 'Learn how to configure GitHub Copilot at user, workspace, and repository levels to optimize your AI-assisted development experience.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-04-02
+lastUpdated: 2026-04-16
 estimatedReadingTime: '10 minutes'
 tags:
   - configuration
@@ -459,6 +459,24 @@ The exported file contains everything needed to view the session without a netwo
 
 **Keyboard shortcuts for queuing messages**: Use **Ctrl+Q** or **Ctrl+Enter** to queue a message (send it while the agent is still working). **Ctrl+D** no longer queues messages — it now has its default terminal behavior. If you have muscle memory for Ctrl+D queuing, switch to Ctrl+Q.
 
+The `/ask` command lets you ask a quick question without affecting your conversation history. The current session context is preserved, so you can use it for one-off lookups without derailing an ongoing task:
+
+```
+/ask What does the `retry` utility in src/utils do?
+```
+
+The `/env` command shows all loaded environment details — instructions, MCP servers, skills, agents, and plugins — in a single view. Use it to verify that the right resources are active for the current session:
+
+```
+/env
+```
+
+The `/statusline` command (with `/footer` as an alias) lets you control which items appear in the terminal status bar. You can show or hide individual indicators like the working directory, current branch, effort level, context window usage, and quota:
+
+```
+/statusline             # show the statusline configuration menu
+```
+
 The `/allow-all` command (also accessible as `/yolo`) enables autopilot mode, where the agent runs all tools without asking for confirmation. It now supports `on`, `off`, and `show` subcommands:
 
 ```
@@ -477,6 +495,18 @@ gh copilot --effort high "Refactor the authentication module"
 
 Accepted values are `low`, `medium`, and `high`. You can also set a default via the `effortLevel` config setting.
 
+### CLI Startup Flags
+
+The `--mode` flag (along with its aliases `--autopilot` and `--plan`) lets you launch the CLI directly in a specific agent mode without waiting for the interactive session to start:
+
+```bash
+copilot --mode agent    # start in agent mode (autonomous tool use)
+copilot --autopilot     # alias for --mode autopilot (allow-all)
+copilot --plan          # start in plan mode (propose without executing)
+```
+
+This is useful in scripts or CI pipelines where you want the CLI to immediately begin working in a specific mode without an interactive prompt.
+
 ## Common Questions
 
 **Q: How do I disable Copilot for specific files?**