Document optional debugger version

Clarify that browser debugger version is optional, but when provided it
should match the immutable deployed build identifier used for browser
build lookup and sourcemap resolution. This keeps the SDK contract
aligned with graceful degradation when no version is configured.

Author: watson

packages/debugger/README.md

@@ -17,10 +17,12 @@ datadogDebugger.init({
   site: '<DATADOG_SITE>',
   service: 'my-web-application',
   //  env: 'production',
-  //  version: '1.0.0',
+  //  version: 'my-deployed-build-version',
 })
 ```
 
+If provided, `version` should be set to the immutable deployed browser build identifier used for source map upload and browser build resolution. If omitted, debugger delivery and snapshots still work, but browser build lookup and source-aware resolution may be unavailable.
+
 If [Datadog RUM][3] is also initialized on the page, debugger snapshots automatically include RUM context (session, view, user action) without any additional configuration.
 
 ## Troubleshooting

packages/debugger/src/entries/main.ts

@@ -88,6 +88,7 @@ export interface DebuggerPublicApi extends PublicApi {
    *   service: 'my-app',
    *   site: 'datadoghq.com',
    *   env: 'production'
+   *   version: 'my-deployed-build-version',
    * })
    * ```
    */