[feat] State reachability and mode together at the top of both pages

[ok]

From testing on a live box: the two pages disagreed about what the top-right pill meant (mode on the members page, reachability on the status page), the mode on the status page was a small pill under a very large verdict, and the members page dressed two pieces of ordinary guidance as yellow warnings.

What changes

• Same header on both pages: a reachability pill and a mode pill, in that order. The members page reads the anonymous status.json for both, so its header is right before a token is entered; with MIRALL_RELAY_ADMIN_UI=false it falls back to today's behaviour (no reachability pill, Locked until unlocked).
• Status hero: the headline names the mode at the same size as the verdict — Reachable Public relay. The member count stays in its tile; the hero repeats it only for the one case that changes what the relay does, Private relay · no members.
• Members page: the bearer-credential advice and the mode notice are hint text inside the Invite someone card instead of note warn boxes. Nothing on that page is toned as a warning now except the error line.
• The reachability labels and tones move into access-copy.js beside the mode wording, so both pages name both things from one definition. verdict() in the status page keeps the sentences.

Testing

• New unit tests for reachabilityPill (including asserted-never-shown-as-measured), the two-pill headers, the hero headline in public / private / empty-private, the plain-text notices, and the members script's snapshot fetch having a failure path.
• Existing tests pass unmodified apart from the one that pinned note warn on the mode notice.
• npm run lint clean, npm test 416/416.
• Looked at both pages in a browser in public and private mode, wide and narrow.