feat: add --download-path option (#536)

* feat: add --download-path option

Adds a `--download-path` flag (and `AGENT_BROWSER_DOWNLOAD_PATH` env / `downloadPath` config key) to set a default download directory for browser downloads.

Without this, Playwright stores downloads in a temp directory that is deleted when the browser closes. The new option passes through to Playwright's `downloadsPath` on `launch()` and `launchPersistentContext()`.

Fixes #507

* improvements

* fixes

* fixes

docs/src/app/commands/page.mdx

@@ -109,6 +109,8 @@ agent-browser download <sel> <path>   # Click element to trigger download
 agent-browser wait --download [path]  # Wait for any download to complete
 ```
 
+Use `--download-path <dir>` (or `AGENT_BROWSER_DOWNLOAD_PATH` env) to set a default download directory. Without it, downloads go to a temporary directory that is deleted when the browser closes.
+
 ## Mouse
 
 ```bash

docs/src/app/configuration/page.mdx

@@ -73,6 +73,7 @@ Every CLI flag can be set in the config file using its camelCase equivalent:
     <tr><td><code>cdp</code></td><td><code>--cdp</code></td><td>string</td></tr>
     <tr><td><code>autoConnect</code></td><td><code>--auto-connect</code></td><td>boolean</td></tr>
     <tr><td><code>colorScheme</code></td><td><code>--color-scheme</code></td><td>string (<code>dark</code>, <code>light</code>, <code>no-preference</code>)</td></tr>
+    <tr><td><code>downloadPath</code></td><td><code>--download-path</code></td><td>string</td></tr>
     <tr><td><code>headers</code></td><td><code>--headers</code></td><td>string (JSON)</td></tr>
   </tbody>
 </table>
@@ -151,6 +152,7 @@ These environment variables configure additional daemon and runtime behavior:
     <tr><td><code>AGENT_BROWSER_AUTO_CONNECT</code></td><td>Auto-discover and connect to a running Chrome instance.</td><td>(disabled)</td></tr>
     <tr><td><code>AGENT_BROWSER_ALLOW_FILE_ACCESS</code></td><td>Allow <code>file://</code> URLs to access local files.</td><td>(disabled)</td></tr>
     <tr><td><code>AGENT_BROWSER_COLOR_SCHEME</code></td><td>Color scheme preference (<code>dark</code>, <code>light</code>, <code>no-preference</code>).</td><td>(none)</td></tr>
+    <tr><td><code>AGENT_BROWSER_DOWNLOAD_PATH</code></td><td>Default directory for browser downloads.</td><td>(temp directory)</td></tr>
     <tr><td><code>AGENT_BROWSER_DEFAULT_TIMEOUT</code></td><td>Default Playwright timeout in ms. Keep below 30000 to avoid IPC timeouts.</td><td><code>25000</code></td></tr>
     <tr><td><code>AGENT_BROWSER_SESSION_NAME</code></td><td>Auto-save/load state persistence name.</td><td>(none)</td></tr>
     <tr><td><code>AGENT_BROWSER_STATE_EXPIRE_DAYS</code></td><td>Auto-delete saved session states older than N days.</td><td><code>30</code></td></tr>