First tagged release of the Plumbline evaluation harness.

Leads with nine fail-open defects, closed in the M9 hardening pass. The most
serious: a target returning entirely blank responses scored a perfect 1.0000
on five suites and the gate returned PASS, exit 0. A verdict produced before
that fix can be a vacuous pass.

Gate at this commit: 459 tests OK on CPython 3.11-3.14; the committed demo
audit reproduces byte for byte; the report matches its own seal; the tamper
drill returns exit 3 then exit 1.