v1.19.0 — co-pilot Phase H: `/ark-loop` (the loop primitive)

Third slice of the co-pilot — the safe, reversible apply loop.

• /ark-loop skill (installed for every detected agent CLI): drives the classified plan in a discardable git worktree — applies one mechanical-safe step at a time, validates with ark-check, keeps on green / rolls back on regression, PROPOSES judgment steps for a human decision, loops until goal.met or no-progress, then reports auto-applied vs proposed vs deferred. The agent edits, Ark validates — code only, never DB/schema, never weakening the gate.
• goal.met added to ark-check --plan --json as the loop's termination signal.

Completes the harness primitives: plan + goal (Phase F) · loop (Phase H). Also fixes an intermittent CI "onTaskUpdate" vitest flake (single-fork test run).

Full notes: CHANGELOG.md.