[Docs] add go snippets to reference pages (#2667)

# why

Missing go snippets in the reference files. Also adding the vitest
change so this is prevented in the future

# what changed

# test plan

<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Adds Go snippets to the missing v4 reference pages, adds a dedicated
WebMCP reference, and exports public v4 TypeScript types. Tightens the
`vitest` docs checker to keep TypeScript, Python, and Go in sync, and
clarifies key defaults and options across the docs. Completes Linear
STG-2801 by adding Go to `locator`, `page`, `context`, `stagehand`, and
`clipboard`.

- New Features
- Added Go tabs with quick starts and API examples to the pages above;
examples include `defer` cleanup and `Page.URL()`. Clarified Go locator
scoping and types: use `*PageLocator` for `Locator`/`IgnoreLocators`;
CSS/XPath only for `observe`/`extract` snapshot scoping (no `text=`
yet).
- Documented `Stagehand.ExperimentalBatch` for Go, including worker
execution model, passing JSON input, page targeting via options, and
timeouts.
- Added a new WebMCP reference (`/v4/reference/webmcp`), linked it from
the WebMCP basics page, and added it to navigation.
- Exported public v4 TypeScript reference types from the SDK (e.g.,
`LocatorClickOptions`, `PageReloadOptions`, `LoadState`, `Caching`) and
added contract tests to verify consumers can import them.
- Strengthened the `vitest` checker: parses Go, validates shared SDK
surface and exact headings/params, enforces one TypeScript/Python/Go tab
per page, flags missing snippets, verifies Go `ParamField` types
(including nested fields) match exported struct fields, and enforces
docs coverage for exported public types.
- Clarified docs: `LoadState` allowed values and defaults,
`context.addInitScript` accepts function/string or `{ path | content }`,
cookie `expires` semantics (`-1` for session), and updated WebMCP links
into Page tools and WebMCP API cards.

- Bug Fixes
- Corrected Go docs for `Response.HeaderValue()` to show `(string, bool,
error)` and clarified header lookup behavior.
  - Formatted Go `Clipboard.Paste` shortcut options for readability.

<sup>Written for commit 761afa9.
Summary will update on new commits.</sup>

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---------

Co-authored-by: Sean McGuire <seanmcguire1@outlook.com>

Author: akeimach

packages/docs/docs.json

@@ -70,6 +70,7 @@
               "v4/reference/context",
               "v4/reference/clipboard",
               "v4/reference/page",
+              "v4/reference/webmcp",
               "v4/reference/response",
               "v4/reference/locator"
             ]