Show a pinned banner at the top of the session view with resource and
runtime diagnostics (skills, prompts, themes, extension load errors) plus
the Anthropic subscription-auth billing notice, recomputed live from the
current runtime so they stay accurate across browser reloads.
Warnings carry an optional dismiss capability; the Anthropic notice is
dismissable and durably suppressed through pi's own anthropicExtraUsage
warning setting. Also fixes the testing-guide skill frontmatter so it
loads.