feat(tools): add --json output and expand invariant coverage in gauntlet.py

[abtonmoy]

Summary

tools/gauntlet.py verifies a running Fortress bundle over raw CDP, but it only checked a small set of surfaces and emitted human-readable text — so it couldn't serve as a CI gate or feed a dashboard. This PR keeps the zero-deps, raw-CDP design and adds machine-readable output plus broader coverage of surfaces the engine already spoofs.

Changes

--json output

A new --json flag emits a single JSON object on stdout and sets the exit code from ok:

{ "surfaces": { ... }, "invariants": { "name": true/false, ... }, "ok": true }

Without --json, the human-readable report is unchanged (same structure, just more lines). Documented in --help and the module header.

Seven new invariants

All are already spoofed by the default persona the bundle launcher injects (packaging/tilion):

Invariant	Check
hardwareConcurrency plausible	present and 1 <= n <= 128
deviceMemory present	a positive number
languages well-formed	a real list, length ≥ 2
timezone is an IANA zone	Intl…resolvedOptions().timeZone contains /
canvas 2D noise present	a flat grey fill reads back perturbed
WebGPU adapter present	navigator.gpu.requestAdapter() returns an adapter
plugins non-empty	navigator.plugins.length > 0

The surface-collection expression becomes an async IIFE so it can await navigator.gpu.requestAdapter(); ws_eval already awaits the returned promise.

Reference sample

docs/gauntlet-sample.json — a passing report for reference (CI/dashboard consumers).

Verification

Running end-to-end needs a compiled bundle via --bundle (see docs/BUILD_NATIVE.md), but the report-assembly logic and JSON shaping were validated against a representative default-persona payload:

• --help lists --json.
• The assembled report is valid JSON with the {surfaces, invariants, ok} shape.
• 7 new invariants added (≥ 6 required); the six existing checks and the default text output are unchanged.
• docs/gauntlet-sample.json parses and has the documented shape.

Closes #12