Scheduling core, state store, CLI and unit tests

One tick polls in-flight runs, posts results, classifies the first line and
moves state/assignee; failures get a structured note with transient retry and
backoff, timeouts are killed and handed over, resume failures and long threads
rebuild with a handoff summary. Then the lowest Todo items are dispatched within
terminal concurrency and serialize groups, and a heartbeat is written.
CLI: tick, new, show, comment, state, assign, smoke, check-config.

cli/agentd

@@ -0,0 +1,9 @@
+#!/usr/bin/env python3
+"""Entry point: agentd tick|new|show|comment|state|assign|smoke|check-config (see agentd/cli.py)."""
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+from agentd.cli import main  # noqa: E402
+
+main()