#4284 Docs: the manual describes the CLI's trial ending and trial ended notices and the notices field in swamp subscription status --json

What changed

swamp-club#4276 (branch 4276) adds a post-command trial notice to the swamp CLI, and adds the notices to swamp subscription status. The manual doesn't describe either yet. The CLI design doc is design/surfaces/account-notices.md in the swamp repo.

The post-command notice. After a command that succeeded, in log mode, the CLI prints at most one notice to stderr, as the last line of output:

ℹ Your Swamp Club trial ends in 5 days (2026-11-07).
  Choose a plan:  https://swamp-club.com/billing

⚠ Your Swamp Club trial has ended.
  Choose a plan:  https://swamp-club.com/billing

• Team trials are named by slug: ⚠ The Swamp Club trial for acme has ended.
• With a day or less left, the ending notice reads ends within a day.
• Who sees it: owners of a collective, and admins of a non-personal one, from GET /api/v1/account/notices. Former customers, licensed, admin and covered collectives see nothing.
• How often:
  • Each notice shows at most once a day.
  • An ending trial switches to ended the moment its end passes, with no network call.
  • "Ended" keeps showing daily until a check finds it resolved.
• No off switch: no environment variable turns it off, CI and SWAMP_NO_INBOX_NOTICE included.
• When it doesn't print: under --json or -q, after a failed command, in nested runs, and in the commands that never show the inbox notice (inbox, subscription, auth, serve, worker, start, dashboard, and gate-exempt commands).
• When the CLI checks:
  • On the inbox's slow commands (workflow run, behavior run / model method run, extension pull, extension push), at most every 15 minutes.
  • On any eligible command while an ended trial is cached, so a purchase clears it soon.
  • Once after swamp auth login, and on swamp subscription status.
• Logout: swamp auth logout deletes the key's cached notices.

swamp subscription status. Both output modes now carry the notices:

• Log mode prints the notice lines between the collectives and the call to action.
• --json adds an optional notices array: kind (trial-ended | trial-ending), slug, name, personal, billingUrl, plus endsAt and daysRemaining for an ending trial. The key is left out when the request fails, so a failure never reads as "no notices".

Pages to update

• content/manual/reference/subscription-commands.md:
  • "JSON output": add the notices field and its entry shape.
  • The log-mode description: mention the notice lines.
  • Add a short section, or a link to a new page, on the post-command trial notice.
• One of:
  • a new reference page, for example content/manual/reference/trial-notices.md, covering the notice text, who sees it, when the CLI checks, that nothing turns it off, and where it never prints; or
  • a section in content/manual/reference/inbox-commands.md next to "The notice", making clear the trial notice is separate and has no SWAMP_NO_INBOX_NOTICE equivalent.
• content/manual/reference/swamp-account-requirement.md, if it describes trials, to link to the above.

Ship this after swamp-club#4276 is released, so the manual matches a released CLI.