Keep excluded benchmark attempts out of public commentary

[janicduplessis]

Problem

The benchmark summary currently publishes attempt counts and descriptions of excluded Android/crash attempts. The user requests keeping failed attempts undocumented publicly for now.

Evidence

The current summary contains Current Android coverage and Current crash coverage paragraphs introduced in #463.

Cause

Publication added exclusion commentary alongside otherwise valid-only results.

Fix idea

Remove those public coverage paragraphs. Preserve valid-only graphs, missing-cell states, general validation methodology, and private immutable investigation records. Do not publish failure timelines or a failure-rate dashboard.

[janicduplessis]

Claimed: docs/benchmark-private-failures-464