feat: OACP v0.4.1

[kiloloop-release]

OACP v0.4.1 — enforce-gate hardening.

Highlights:

• Session-scoped envelope enforcement: compiled envelopes bind to the compiling harness session; concurrent sessions in the same repository no longer inherit a dispatched task's constraints or budgets.
• oacp doctor gates enforce-mode signing readiness on trust-pin completeness, with per-receiver gap reporting.
• The Claude envelope hook classifies quoted shell segments correctly (no false escalation on literal pipes / continuations) and tags every ask/deny reason with a stable [oacp-envelope] prefix.
• Signing-only receiver configs preserve conservative always_pause autonomy defaults.
• The autonomy gate evaluator persists complete, lock-serialized audit records.

Message signing remains warn-mode by default — enforcement lands in a later release.

Full details in CHANGELOG 0.4.1.