v0.7.9 — runtime authority separate from model capability

Adds harness-owned authority levels (observe/contribute/operator/admin, default
operator) independent of model passports and ladder tier, configured via
FORGE_AUTHORITY. Authority is checked before interaction mode and cannot be
expanded by a stronger escalated model. The constrained grammar is narrowed
before generation and re-enforced after parsing for advisory engines; denials
log actual/required authority and project into the canonical protocol as
AuthorityDenied → DIAGNOSE (recovery to PLAN). Admin-only shell is scoped to
genuinely dangerous patterns — sudo, remote-script pipes, secret-store reads,
forced git history, and recursive-force deletes aimed at root/home/an absolute
path — while everyday-safe commands (env, rm -rf of a project subdir) stay at
operator. Read-only fleet_send target=list remains available to observers.