Update markdown to v1 and fix CLI reference links (#13166)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [markdown](https://redirect.github.com/wooorm/markdown-rs) |
dependencies | major | `0.3.0` -> `1.0.0` |

---

### Release Notes

<details>
<summary>wooorm/markdown-rs (markdown)</summary>

###
[`v1.0.0`](https://redirect.github.com/wooorm/markdown-rs/releases/tag/1.0.0)

💯

Nothing changed since the last alpha.
It’s just that: this crate’s now being used a bunch and working well, so
it’s time to be stable!

</details>

---

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crates/uv-dev/src/generate_cli_reference.rs

@@ -24,7 +24,7 @@ const REPLACEMENTS: &[(&str, &str)] = &[
     // TODO(zanieb): In general, we should show all of the environment variables in the reference
     // but this one is non-standard so it's the only one included right now. When we tackle the rest
     // we can fix the formatting.
-    (" [env: &quot;UV<em>PYTHON</em>DOWNLOADS=never&quot;]", ""),
+    (" [env: &quot;UV_PYTHON_DOWNLOADS=never&quot;]", ""),
 ];
 
 const SHOW_HIDDEN_COMMANDS: &[&str] = &["generate-shell-completion"];