v7.1.3 Iter Beal Not Route E Corrected

Docs-only. No Lean change. Corrects an error introduced in v7.1.2: docs/OPERA_NUMERORUM_LINKS.md and this README's 'wider work' section labeled the Beal Conjecture as 'Route E', implying it was a fifth entry in the Riemann Hypothesis Route A-D lettering. That is wrong: the Beal Conjecture is its own chamber of Opera Numerorum, spanning two companion repositories (this repository and beal-level-26-foundations), unrelated to the RH routes beyond both being chambers of the same wider project.

docs/OPERA_NUMERORUM_LINKS.md restructured: Beal now under its own heading 'The Beal Conjecture — housed in two companion repositories, level-26 unconditional none'; Routes A-D grouped under their own parent heading 'The Riemann Hypothesis — four independent routes' as #### Route A .. #### Route D. Same restructuring applied to the mirrored section in README.md.

check-v11-release.sh OK: all required DOI strings and 'conditionally complete' remain present elsewhere in README.md; no grep lock broken.