Research: exclude P112 5,6^8 with an affine cover transfer

[petalas]

Summary

P112 TWOSIDE (6,3), profile 5,6^8
  rank-five support <=12
  -> rank-four flat plus <=4 coordinates
  -> existing weighted A6 floor 141 > endpoint allowance 140
  -> one new maximal profile excluded

Adds only research/p112-a6-five-flat/, with a characteristic-zero proof,
exact receipt, immutable source copies and a registered standard-library replay.
The new affine cover transfer lets the actual rank-five support use the existing
weighted theorem. The mixed branch already requires 142. The six original
profiles without weight seven are dominated; five smaller shapes already have
other exclusions and are not counted as new results.

Canonical investigation.
Credit DreamingOfClouds/#3154 at 708f0ad8928c383de8294aea3c126e9461d2066d
for TWOSIDE, Nick Petalas/#3186 at 92675b36a8e0ea41b40f0bcda2a3dd9f313abb0e
for the retained weighted and endpoint bounds, and the retained E8/P112 lineage,
including #3176 and joaqcoo's model. Source pins and applicability checks are in
SOURCES.json.

Evidence

• Before, the original filter retains 5,6^8; the arbitrary forty-cut root
  relaxation gives 137 against allowance 140. After, the affine transfer gives
  the required 141, while the mixed branch gives 142.
• Exhaustive constructive/oracle check of all 64,839 admissible four-cube
  supports; all 560 thirteen-point failure controls reject. The twelve-point
  threshold and four extra points are sharp.
• Registered Python 3.12 replay and fourteen optimized behavioral groups pass.
  Geometry, all 3,309,747 five-flats, all 788,035 six-flats, both endpoint
  branches and the existing weighted cover are replayed. Applicable Ruff
  diagnostics and warnings-as-errors compilation pass.
• The exact final committed export passes the mathematical replay and all fourteen
  tests under optimized Python 3.13 from read-only, Git-free source. That check
  exposed and fixed one disposable-copy permission issue. All 22 committed
  package/input byte comparisons pass. Published head is
  79864770165fe0d7b72c864be4d5a6e2af5e35b5.
• Internal mathematical and artifact reviews found no remaining blocker. The
  standard Weyl-chamber theorem, rational-kernel classification and original
  decoder reduction remain written dependencies. Hosted CI and independent
  human/proof-kernel review are separate.

uv run --python 3.12 --no-project python -W error -B scripts/research_package.py \
  --package research/p112-a6-five-flat

No full C5, complete decoder-floor, supplier or kappa claim. The selected
frontier and frozen canonical inputs are unchanged. Open next questions and
implementation bounds are recorded in the package.

Merge Danger

Door: two-way.

Blast Radius: research.

One isolated opt-in proof package. No shared-code or selected-result changes.