Update mz-docs skill from materialize@main - #88

The rc.4 increment is two items, both omitted, so this snapshot adds no
entry to the assembled `## v26.45.0` section and the provisional dates are
unchanged (Cloud 2026-10-08, Self-Managed 2026-10-09).

- #39549 pins jemalloc's allocator page back to 4 KiB on
  aarch64-unknown-linux-gnu, repairing a 64 KiB-page regression that #39339
  introduced earlier in this same unreleased train. No released version ever
  ran the 64 KiB page, so a user upgrading from v26.44.0 sees the same
  allocator page before and after; #39339 was itself omitted at rc.1 as a
  dependency bump, so nothing published describes the behavior and there is
  no bullet to amend. Recorded as borderline in the snapshot's omitted.md.
- `ba9b30921` is the materialize-bot version bump for the candidate.

The one agent-skills PR in the window, MaterializeInc/agent-skills#88, is an
automated `mz-docs` regeneration and is omitted as it was at rc.1.

This empty commit records rc.4 as applied; v26.39.0 rc.3 is the precedent for
a zero-entry RC on this layout.