fix(scheduler): address review findings

- JobScheduler: a stored job whose zone lookup throws no longer fails StartAsync; timer re-armed under the lock;
  a delivery cut off by shutdown isn't recorded (one-offs fire again after restart); CancelJobAsync in one step
- Schedules.ParseAt: ISO 8601 with a date only (no machine-clock date for a bare 09:00)
- core: a FollowUp prompt that loses the race to a starting run joins it as a follow-up, not steering
- Telegram: TimeZoneFor tolerates non-numeric targets; RunPromptAsync waits only when queued; one agent dir
- ScriptRunner: bad workspace paths are Failed, not exceptions; zone id helpers share TimeZoneIds.ToIana's rule
- tests: no wall-clock sleeps in scheduler tests; transcript-entry, disabled-scheduler and failing-prompt coverage
- docs: spec notes for the above; README row for the scheduler

README.md

@@ -18,6 +18,7 @@ Claude Code as a model provider without an API key.
 | OpenAI-compatible provider | `extensions/Volcanic.AgenticCore.Extensions.OpenAI` | OpenAI, OpenRouter, Groq, Ollama, llama.cpp, vLLM |
 | Claude Code (subscription) provider | `extensions/Volcanic.AgenticCore.Extensions.ClaudeCode` (+ `.Bridge`) | Spawns `claude -p`, MCP "proposal" bridge |
 | Google Calendar (tool + connect commands) | `extensions/Volcanic.AgenticCore.Extensions.GoogleCalendar` | `GOOGLE_CLIENT_ID`, `GOOGLE_CLIENT_SECRET`; one account per chat |
+| Scheduler (reminders, scheduled prompts, watcher scripts) | `extensions/Volcanic.AgenticCore.Extensions.Scheduler` | Cronos; per-chat jobs in `<agent dir>/scheduler/jobs.json`; see [docs/telegram-bot.md](docs/telegram-bot.md#scheduling) |
 | Telegram bot | `hosts/Volcanic.AgenticCore.Telegram` | Chat with the agent from Telegram; long polling, Claude Code, allow-list |
 | Reference headless host | `samples/Volcanic.AgenticCore.Sample.Headless` | Prompt in, JSON events out |
 | Tests | `tests/` | xunit; no test calls a paid API |