v2.65.6 — Sprint 136: documentation refresh (docs only)

Documentation only; no source, wire-format, or output change (the tree
compiles to a v2.65.5-identical binary). Brings the docs current after
the v2.65.1-v2.65.5 releases:

• README: regenerated the head-to-head table and win/loss notes from a
  fresh v2.65.6 measurement (ratios unchanged since v2.65.0 — output is
  byte-identical — with corrected decode-speed comparisons and the
  vv-extreme encode-speed column now ~2 MB/s per v2.65.2); replaced the
  out-of-order, incomplete version-notes pile with a clean
  newest-first "recent releases" summary through v2.65.6.
• DEPLOY.md: corrected stale release-artifact names that were still
  pinned to 2.61.1 (tarball, bundle, binary, and vcpkg version) while
  the release is v2.65.x.
• bench/COMPARISON.md: added a currency note that the v2.65.0 tables
  hold through v2.65.6 (byte-identical output), with extreme encode
  speed the only moved column.
• SECURITY.md: document version to 2.11 / codebase v2.65.6.

Verified: reference-decoder guard passes, ratio gate +-0, current build
clean.