v2.65.1 — Sprint 131: OF-code price decomposition (negative result, default off)

Maintenance release. Output is byte-identical to v2.65.0 across the
full corpus, the ratio gate (±0), and the fixture suite; the wire
format is unchanged.

The optimal parser's match price is refactored into an explicit
decomposition — 8 (LL+ML sequence overhead) + OF-code bits + offset
extra bits — with the previous constants preserved exactly as the
prior (rep codes 2 bits, explicit codes 6 bits). The greedy prepass
now also classifies each match's OF code with the wire's exact rep
rules, producing a per-block OF-code histogram, and a new
VV_OPT_OF_BLEND knob (default 0) can blend measured code costs into
the price the way VV_OPT_LIT_BLEND does for literals.

The measured result is negative and is recorded so it is not re-tried
blind: blend 0 (the prior) beats every measured blend on the 11-file
corpus total (blends 2/4/6/8 of 8 land 0.01-0.08% worse). Measured OF
pricing helps plain text and source (~-1%) but hurts json and logs by
more — per-block OF distributions on this corpus do not deviate from
the prior enough to pay, unlike the literal distributions in v2.64.0/
v2.65.0. Blend 0 was verified to reproduce v2.65.0 byte-for-byte
before the sweep, so the refactor itself is exactly anchored.

Validation: 22/22 test suites under -O3 -flto; ratio gate ±0 bytes
(output identity); 5,200 differential fuzz cases consistent.