fix: correct Exercise 1 numbering and align partials convention with practice

- cli/1-install-copilot-cli.mdx: title was 'Exercise 2' and the
  next-lesson sentence pointed to 'Exercise 3'. The CLI overview
  correctly lists this lesson as Exercise 1 and the next as Exercise 2.
  Renumber both. Workshop/ regenerated to match.
- partials.instructions.md: previous guidance said callout partials
  must NOT import Aside (host page imports it). Every existing
  callout-*.mdx contradicts this — they all import Aside themselves.
  Reverse the guidance to match practice: callout partials are
  self-contained and import their own Starlight components.

Both findings surfaced in Copilot's PR review on #140.

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

Author: GeekTrainer

.github/instructions/partials.instructions.md

@@ -45,6 +45,14 @@ If a partial drops into the middle of a numbered list, write its items as plain
 1. Third step.
 ```
 
-## No `<Aside>` imports inside callout partials
+## Imports inside callout partials
 
-When the partial *is* a single `<Aside>`, the import for `Aside` lives in the host MDX page. The partial just contains the JSX. (Imports inside partials are allowed but the convention is to keep partials minimal.)
+Callout partials should be **self-contained**: import any Starlight component they use (typically `Aside`) at the top of the partial itself, rather than expecting the host page to provide the import. This matches how every existing `callout-*.mdx` is written and means a host page can drop in a callout partial without remembering to also add an `import { Aside } ...` line.
+
+```mdx
+import { Aside } from '@astrojs/starlight/components';
+
+<Aside type="tip" title="Start a Copilot CLI session">
+  …
+</Aside>
+```

docs/src/content/docs/cli/1-install-copilot-cli.mdx

@@ -1,5 +1,5 @@
 ---
-title: "Exercise 2 - Installing GitHub Copilot CLI"
+title: "Exercise 1 - Installing GitHub Copilot CLI"
 ---
 
 import { Aside } from '@astrojs/starlight/components';
@@ -106,7 +106,7 @@ Congratulations! You've successfully installed and authenticated GitHub Copilot
 - trust a directory for Copilot CLI to work with.
 - verify the installation is working correctly.
 
-Now that Copilot CLI is installed, let's see how it picks up your repository's custom instructions. Continue to [Exercise 3 - Custom instructions hands-on][next-lesson].
+Now that Copilot CLI is installed, let's see how it picks up your repository's custom instructions. Continue to [Exercise 2 - Custom instructions hands-on][next-lesson].
 
 ## Resources