Support scheduled chat delivery

[pmbstyle]

Summary

• Add optional scheduled task delivery targeting for the current chat or an explicit runtime chat ID.
• Allow signed explicit delivery chat IDs while keeping the existing configured fallback behavior unchanged.
• Treat only chat ID 0 as internal for worker follow-ups so negative channel IDs can receive scheduled updates.
• Add Telegram setup docs for optional scheduled group updates and ignore generated cache directories.

Validation

• uv run ruff check src/octopal/runtime/octo/followup_pipeline.py tests/test_heartbeat.py src/octopal/runtime/octo/scheduler_helpers.py src/octopal/runtime/scheduler/service.py src/octopal/runtime/octo/scheduled_runtime.py src/octopal/tools/catalog.py tests/test_scheduler_safety.py
• uv run pytest tests/test_heartbeat.py tests/test_scheduler_safety.py
• uv run pytest