The Backups page opens with one line: "Recoverable now", or the first thing that stands in the way #2146

Split from #1986 (the owner's ask in #1147: know at a glance whether the forge can come back).

Done looks like:

• [ ] At the top of /settings/backups, one line built from four facts the page already has: the store is reachable, the newest snapshot is under 26 h old, the key is carried, and the last drill is green and under 8 days old.
• [ ] If all four hold it reads "Recoverable now" with a check icon. Otherwise it names the first one that fails, in plain words (for example "Not recoverable now: the newest snapshot is 3 days old").
• [ ] Every value is escaped, and the line adds no request beyond what the page already does.
• [ ] Tests: one case per failing fact, plus the all-good case, each asserting the exact sentence.

Files: src/web/pages/backups.ts and its test. Risk: the store reachability probe must not slow the page, so reuse the cached state the page already reads. Brief: scout.