Document astro dev --no-lock flag

src/content/docs/en/reference/cli-reference.mdx

@@ -125,6 +125,7 @@ Flags
 --host <custom-address>  Expose on a network IP address at <custom-address>
                --open  Automatically open the app in the browser on server start
               --force  Clear the content layer cache, forcing a full rebuild.
+            --no-lock  Start the dev server even if another one is already running, without checking or writing the lock file.
           --help (-h)  See all available flags.
 ```
 
@@ -212,6 +213,20 @@ astro dev --background --force
 
 <ReadMore>See [Background mode for AI coding agents](/en/guides/build-with-ai/#background-mode) for more about automatic agent detection and the health endpoint.</ReadMore>
 
+#### `--no-lock`
+
+<p><Since v="7.1.0" /></p>
+
+Starts the dev server without checking or writing the lock file used to detect other running dev servers. This allows a new dev server to start alongside one that's already running for the same project, instead of erroring.
+
+```shell
+astro dev --no-lock --port 4322
+```
+
+The new server is not tracked by `astro dev stop`, `astro dev status`, or `astro dev logs`.
+
+When combined with `--background` (including when triggered by an AI coding agent) or `--force`, an error is throwned, as both rely on the lock file.
+
 <h3>Subcommands</h3>
 
 <p><Since v="7.0.0" /></p>