feat(monitor): add monitor primitive with poll-until-finalizer and state persistence

[jorisjonkers-dev-agents]

Summary

Adds a first-class monitor CLI command to the council orchestrator that replaces ad-hoc background polling loops with a structured, owned primitive.

• monitor start --name <n> --interval <dur> --deadline <dur> --cmd <probe> --until <predicate> --then <finalizer> --exec-dir <dir> — synchronous poll loop; on predicate match runs the finalizer in the same process; on deadline fails loudly with last probe output
• monitor status --name <n> --exec-dir <dir> — reads and prints current state from monitors/<name>.json
• monitor list --exec-dir <dir> — lists all monitors with dead-monitor detection (last tick >2.5x interval ago while still polling)

Built-in probes: probe:actions-runs-for-sha, probe:pr-mergeable, probe:ghcr-package-visible.

State file persisted at <exec-dir>/monitors/<name>.json with fields: name, status, startedAt, deadline, lastTickAt, lastOutput, intervalMs, cmd, until, then.

Fixes #19

Test plan

• 64 test files, 644 tests pass (npm test in council/ts/)
• TypeScript type check clean (tsc --noEmit)
• Domain unit tests: parseDuration, isMonitorDead, evaluatePredicate
• Workflow tests: predicate-match→finalizer, deadline timeout, state file shape, dead-monitor detectability
• CLI routing tests: monitor start/status/list subcommands
• Composition integration tests: CouncilApp.monitor wiring