Add three-arch Artemis stress campaign serial logs (audit artifacts)

Serial logs for the 30-replicate ART-STRESS-CAMPAIGN run, one per
architecture:

  logs/20260802-160052/amd64    30 reps x 50 trials, 1500/1500 pass
  logs/20260802-173226/aarch64  30 reps x 50 trials, 1500/1500 pass
  logs/20260802-181803/riscv64  30 reps x 50 trials, 1500/1500 pass

4500 trials, zero failures. These are the audit trail for the claim that
the block_words.c stale-pointer cache-aliasing fix holds at scale, and for
cross-arch disk read/write/persistence.

Committed as raw blobs, matching the ~6.7GB of existing log objects in
history. Note that .gitattributes already declares logs/**/*.log and the
bare-metal CSVs as LFS-tracked, but git-lfs is not installed in this
environment, so those filters are silent no-ops -- the 744MB log at
logs/20260802-115945/ is likewise a raw blob, not a pointer. Flagged for a
proper fix (install git-lfs, confirm server-side LFS support, decide
whether to migrate existing history) rather than half-applying LFS to only
these three files.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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