Expose browser pool viewport

[IlyaasK]

Summary

• expose computed nested viewport on kernel_browser_pool
• preserve omitted viewport as a typed null object
• require positive width/height and optional positive refresh rate
• reject explicit null, malformed objects, missing dimensions, and invalid child values
• update generated Registry docs

Scope

Additive v1 durable read state only. Chrome policy and live acceptance remain separate; no runtime/session fields are exposed.

Tests

Ran focused tests repeatedly, race tests, full short suite, vet, gofmt, module checks, Terraform example fmt, docs drift, and diff checks.

Coverage includes Framework nested-state roundtrip, typed-null omission, omitted refresh rate, malformed/null viewport, missing and non-positive dimensions, invalid refresh rate, and wrong JSON types.

Acceptance not run; live viewport payload behavior remains for the opt-in acceptance slice.

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Note

Low Risk
Additive read-only data source field with validation and tests; no auth, writes, or runtime pool behavior changes.

Overview
Adds a computed nested viewport attribute to the kernel_browser_pool data source so Terraform can read durable pool browser window settings from the API.

When the API omits viewport, state uses a typed null object; when present, width and height must be positive and refresh_rate is optional but must be positive if sent. Malformed or invalid viewport payloads (explicit null, wrong types, missing dimensions, non-positive values) surface as read diagnostics instead of silent bad state. Registry docs for the data source are updated, with unit tests covering happy paths and rejection cases.

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