docs: add ! shell functionality reference to lesson 14 (Session Management)

Co-authored-by: calebwilson706 <71669491+calebwilson706@users.noreply.github.com>

Author: Copilot

tutorial/lessons/14-session-management.md

@@ -55,6 +55,17 @@ This shows a visual breakdown of token usage — how much is taken by system pro
 
 This shows request counts, token usage, and other session metrics.
 
+### Running shell commands with `!`
+
+You can run a shell command directly from within your Copilot session using the `!` prefix:
+
+```
+!git status
+!ls exercises/sample-app/src
+```
+
+This is useful when you want a quick terminal check — listing files, checking git state, verifying an environment variable — without asking Copilot to do it for you. The output appears inline and Copilot can see it too, so you can follow up with a question about the result.
+
 ### When to start fresh
 
 Sometimes it's better to start over than to correct course: