#2501 Remove internal diagnostic methods

Removes ping, runtimeLoopbackStatus, and browserGetVersion from the protocol and all SDK surfaces. It also removes the extension and runtime handlers and refreshes generated clients and documentation.

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Summary by cubic

Removed internal diagnostic methods (ping, runtime.loopback_status, and browser.get_version) from the v4 protocol and all SDKs to align the public surface with Linear STG-2708. Docs, generated clients, and tests were updated; metrics remain available.

• Refactors

  • Protocol/Server: Removed methods and schemas from stagehand.v4.json and the registry; deleted related controllers/handlers (including browserController) and router routes; tightened the request schema; dropped runtime helpers that exposed these diagnostics.
  • SDKs (TS, Python, Go): Removed corresponding APIs and types; regenerated models/clients; updated tests to use non-diagnostic calls (e.g., context.pages or stubbed test.request) and adjusted notification/log checks.
  • Docs: Removed diagnostics from the stagehand reference and first-steps intro; clarified that only metrics are built in.

• Migration

  • Remove any usage of stagehand.ping(), stagehand.runtimeLoopbackStatus(), and stagehand.browserGetVersion() (and equivalents in Python/Go).
  • For connectivity, await stagehand.init() and handle errors. For browser version, query CDP Browser.getVersion via your own connection. stagehand.metrics() is unchanged.