T9: the pasture as plugins

tools/pasture/run.sh up [peer...] | down | logs | ps and interop.sh [peer...] are now built
from parts:
- lib/pasture.sh: network, Caddy with its CA in a volume and copied to .ca/root.crt, Mongo,
  PrivaPub;
- peers/<name>.sh: each peer's <name>_up;
- lib/interop.sh: ok, ko, and xf for checks expected to fail until a later phase;
  privapub_token <persona>, which gives each peer its own persona under one root; and
  stats_check;
- scenarios/<name>.sh: each peer's checks.

GoToSocial is pinned at 0.22.1, the version the 33 checks were proven on. Its scenario
gains four statistics checks:
- the admin statistics describe gts.test as gotosocial;
- they count inbound and outbound traffic;
- they name no account.

37/37 passed three runs in a row.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

.gitignore

@@ -403,3 +403,5 @@ PrivaPub/media-store/
 PrivaPub/media-store-proxy/
 tools/pasture/.publish/
 .claude/worktrees/
+tools/pasture/.ca/
+tools/pasture/.state/