feat(bake): add cross-platform just bake-day recipe for daily v0.6.0 bake-period checks

[githubrobbi]

Closes the operator-ergonomics side of the v0.6.0 one-week main bake gate described in
docs/architecture/memory-tiering-bake-criteria.md
§1.1 / §1.2 / §1.3.

Motivation

The bake-criteria doc requires running just readiness + a tracing-log
red-flag audit every weekday on both Mac and Windows for 7 consecutive
weekdays. Previously this was a manual multi-step sequence — separate
tee / Tee-Object invocations, separate grep / Select-String
audits per platform, separate row-format-by-hand for §4 of the bake
log. just bake-day collapses it into one command on both platforms.

What the recipe does

1. Creates $HOME/uffs_bake/ if missing.
2. Runs just readiness, tee'd to $HOME/uffs_bake/<date>-<platform>.log.
3. Asserts exit code 0 AND the 150/150 steps passed final line.
4. Greps the log for §1.3 red-flag patterns:
   • panic / OutOfMemoryError / FATAL / abort
   • BackgroundIoPriority...begin failed (Phase 5 health signal)
5. Prints a PASS/FAIL summary plus a copy-pasteable row for §4 of the
   bake-criteria doc, with the other platform's column marked
   (pending) so a Mac + Windows run on the same day merges cleanly.

Exits 0 on green, 1 on any failure. Re-runs are idempotent — the
day's log is overwritten so the latest pass-attempt is always the
recorded one.

Same command on both platforms

just bake-day          # Mac → ~/uffs_bake/<date>-mac.log

just bake-day          # Windows → ~/uffs_bake/<date>-windows.log

Sample output (Mac, all-green case)

🎂 Bake-day check — mac — 2026-05-15
   Log: /Users/rnio/uffs_bake/2026-05-15-mac.log

… [full readiness output tee'd to log] …
══ ALL GOOD ══  150/150 steps passed

── Bake-day summary ─────────────────────────────────
✅ mac 2026-05-15 — ALL GREEN (150/150)

── Paste row into docs/architecture/memory-tiering-bake-criteria.md §4 ─
|  ?  | 2026-05-15 | full readiness | 150/150 ✅ | full readiness | (pending) |       |

The Windows run produces the mirror row, so the two runs merge cleanly
into one row by replacing the (pending) cells.

Platform variants

• [unix] — bash, tee for capture, grep -F/-E for the audits.
• [windows] — PowerShell, Tee-Object, Select-String -SimpleMatch/-Pattern.

Both produce the same on-disk artefact shape and the same console
summary format.

What this unblocks

The remaining v0.6.0 release-gate work per
memory-tiering-bake-criteria.md
§3 is purely the 7-consecutive-weekday observational hold plus the
four sign-off items (CHANGELOG finalize, release notes draft, manual
diff review, no open critical issues).

Verification

• just lint-pre-push — 23/23 gates green (50s pre-commit; 47s pre-push).
• just --summary | grep bake-day — recipe registered correctly.
• just --list | grep bake-day — appears in operator listing with the
  conventional last-comment-line summary, matching the sibling
  readiness / soak / tier-compare recipes.

Files touched

• just/dev.just — single recipe addition ([unix] + [windows]
  variants under one logical name). +122 lines, no deletions, no
  other recipes affected.