Add Q26 symmetry-parity shell reduction

[jkolantree]

Summary

• Publish a complete structural reduction for a hypothetical thirteen-queen dominator of the 26 by 26 board.
• Reproduce the coarse orbit counts (16, 91, 49), totaling 156 canonical parity-profile shells.
• Apply Weakley's empty-line parity lemma to obtain the tightened counts (15, 78, 49), totaling 142 shells.
• Retain a dependency-free canonical generator, complete deterministic JSON roster, an independently executable compact reproducer, and positive and fail-closed tests.
• Link the reduction from the existing Q26 attack note and correct the attribution of Dmitry Kamenetsky's OEIS upper-bound witness.

Evidence and correction boundary

An earlier public summary incorrectly described the 156 shells as exhaustively searched cases. No retained Q26 solver run returned UNSAT; the published runs remain UNKNOWN.

A shell records only an occupied-line-count type and occupied-line parity counts. It is not a queen placement or SAT instance. The 156-shell quotient, and its 142-shell tightening, are exhaustive as structural coverage maps only.

This PR does not:

• prove any shell realizable or unsatisfiable;
• replay the absent historical case expander or solver campaign;
• exclude a thirteen-queen dominator;
• establish gamma(Q26) = 14;
• claim novelty or priority for an exact domination number.

The supported status remains 13 <= gamma(Q26) <= 14.

Verification actually executed

• Independent theorem-bridge and Burnside-count reviews against Weakley's primary paper: PASS.
• Q26 attack plus profile tests: 29/29 PASS.
• New profile tests: 9/9 PASS, including missing/duplicate/altered-roster, weakened-Lemma-6, deterministic serialization, and overwrite rejection.
• Complete unit discovery: 265 tests PASS, 1 Windows symlink-privilege test SKIPPED.
• Canonical 156/142 JSON roster check: PASS.
• Manifest regeneration and verification: PASS, 122 files.
• Normal checkout, linked worktree, and fresh Git archive inventory agreement: PASS, 122 files.
• F8, F10, F11, F12, and F13 fixture checks: PASS.
• Markdown-math checker: PASS.
• git diff --check: PASS.
• Exact eight-path publication allowlist: PASS.

PDF build verification was not run locally because this environment has no make, latexmk, or tectonic; no paper, synopsis, or PDF files change.

GitHub checks

• verify: PASS.
• build-pdfs: PASS.

Unchanged authority

No BSC claim or fixture identifier, ROADMAP order, ledger, fixture, paper, PDF, release metadata, workflow, tag, release, DOI, Zenodo record, ruleset, or repository setting is changed.