t3: pin t3@0.0.24 + stop nightly auto-update (auth-outage fix) [ci skip]

The t3-autoupdate timer (re-enabled by the provisioner's step 5b with
`--now`, which fires the missed daily job immediately on a Persistent
timer) pulled t3@nightly 0.0.25 mid-day. That build ran forward schema
migrations on every ~/.t3 state.sqlite (auth_pairing_links/auth_sessions
role->scopes, +proof_key_thumbprint) AND changed the bootstrap API,
breaking t3-mint/pairing for ALL devvm users (pair prompt, no session).

- t3-autoupdate.sh: now a pinned-version ENFORCER (T3_PIN=0.0.24), not a
  nightly tracker -- re-asserts the pin (a no-op when correct).
- t3-provision-users.sh step 5b: drop `--now` (it triggered the
  immediate missed-job run that pulled the bad build).
- setup-devvm.sh: install pinned t3@0.0.24 at machine setup.
- unit Descriptions + service-catalog reflect the pin.
- post-mortem: 2026-06-09-t3-nightly-autoupdate-auth-outage.md.

Host already reconciled out-of-band: rolled back to 0.0.24, re-enabled
the (now-pinned) enforcer, reset the 2 new users' disposable DBs,
surgically reverted wizard's auth tables to level-30 (96 threads + live
session preserved). All users verified 302 + t3_session.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/t3-autoupdate.timer

@@ -1,5 +1,5 @@
 [Unit]
-Description=Daily t3 nightly auto-update
+Description=Daily t3 pinned-version enforcer (re-asserts T3_PIN; no-op when correct)
 
 [Timer]
 OnCalendar=*-*-* 04:00:00