Aperture: a small source member with a few stray NUL bytes is excluded as binary #4351

Problem

Gate 3.1's NUL-density test in gitgalaxy/core/aperture.py (nuls * 1000 > len(content)) rejects short members. A 250-byte member with 2 NUL bytes is over 1 per 1000, so the whole member is recorded as "Blocked (Binary Format Detected)" and disappears from every fact channel. Stray NULs are common in members transferred from a mainframe (#3534 / ledger D016).

Evidence

estate/apps/NORD/pli/NULREST.pli at estate-crucible v0.3.0: a 7-line PL/I member with two NULs at the end of its first comment is blocked. Horror H-0037.

Impact

The member vanishes from the scan silently: its units, calls and copybooks are missing, and nothing reports a parse problem. Any short member is at risk.

Acceptance criteria

• A member that decodes as text and holds only a handful of NULs (e.g. ≤ 4) stays source, whatever its size. Genuine binaries are still blocked.
• Regression test with a short member plus 1-2 NULs, and a real binary.

Related: #3534 (D016).

Found by estate-crucible v0.3.0 phase 2 (#4317, #3988): planted in squid-protocol/estate-crucible, scored by tests/tools/estate_crucible.py on main (scorecard in #4347). The horror flips to pass when this is fixed.