Add coverage for render reveal ordering and debug timing diagnostics

[tabmail-kmyi]

Why

Coverage follow-up deferred from #142 at the owner's request so the rendering fix can merge. The full native suite completed with no unexpected failures, and the independent production-code reviews found no required corrections. These are missing regression assertions, not identified production defects.

Scope

• Fit before reveal: extend the native reveal fixture to exercise the production first-layout fit/reveal sequence. Observe the loading state before commitment and its dismissal after committed content fits; ensure the fit and reveal acknowledgements cannot consume each other's allowance.
• Native timing output: verify enabled output, per-load identity and stage order, unchanged wrapped content, initial disabled silence, and silence after logging is disabled on an existing clock. Reuse the existing logging-state and hosted-render fixtures.
• Resource values: use input-sensitive URL fixtures with distinct origins. Assert origin, kind, start, duration, response-start, and transfer values, including zero/unavailable timing fields. Preserve assertions for bounded output, URL-path/query redaction, and absence of additional requests.

Acceptance

Add focused regressions that fail when the corresponding behavior is removed or corrupted. Keep this work scoped to the three coverage gaps and reuse existing fixtures. Any newly discovered production defect should be tracked separately.