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

cli/src/output.rs

@@ -2106,6 +2106,7 @@ Options:
   --cdp <port>               Connect via CDP (Chrome DevTools Protocol)
   --auto-connect             Auto-discover and connect to running Chrome
   --color-scheme <scheme>    Color scheme: dark, light, no-preference (or AGENT_BROWSER_COLOR_SCHEME)
+  --download-path <path>     Default download directory (or AGENT_BROWSER_DOWNLOAD_PATH)
   --session-name <name>      Auto-save/restore session state (cookies, localStorage)
   --config <path>            Use a custom config file (or AGENT_BROWSER_CONFIG env)
   --debug                    Debug output
@@ -2148,6 +2149,7 @@ Environment:
   AGENT_BROWSER_AUTO_CONNECT     Auto-discover and connect to running Chrome
   AGENT_BROWSER_ALLOW_FILE_ACCESS Allow file:// URLs to access local files
   AGENT_BROWSER_COLOR_SCHEME     Color scheme preference (dark, light, no-preference)
+  AGENT_BROWSER_DOWNLOAD_PATH    Default download directory for browser downloads
   AGENT_BROWSER_DEFAULT_TIMEOUT  Default Playwright timeout in ms (default: 25000)
   AGENT_BROWSER_SESSION_NAME     Auto-save/load state persistence name
   AGENT_BROWSER_STATE_EXPIRE_DAYS Auto-delete saved states older than N days (default: 30)