chore(governance): increase idle community discovery cadence

[qqqys]

Summary

Increase registered-source community discovery from once every 24 hours to once every 2 hours, with at most 1 hour of lateness, while preserving normal development as the higher-priority path.

The coordinator contract now selects community discovery only after recovery, intake, resumable PR/CI/post-merge work, roadmap decomposition, and executable issues are exhausted. A due scan that is blocked remains pending until the next truly idle tick. Daily global dogfood keeps its existing 24-hour cadence and 6-hour lateness behavior.

Reviewer Test Plan

• Confirm a due community scan is selected only when no lease, resumable delivery work, intake or promotion, normalized ready work, agent-ready issue, or roadmap decomposition remains.
• Confirm a blocked due scan stays pending and runs on the next truly idle coordinator tick.
• Confirm registered sources remain the only permitted discovery inputs.
• After merge and runtime reconciliation, confirm qrun validate-contract and qrun verify pass and that the durable scheduler records the next due time without rewriting the ledger.

Validation

• Focused community governance test: 3 passed
• Typecheck: passed
• Build: passed
• Full unit suite: 83 files, 1677 tests passed
• Diff/format checks: passed

中文说明

将仅限注册来源的社区发现频率从每 24 小时提高到每 2 小时，最大延迟 1 小时；只有在 lease、PR/CI/post-merge、用户 intake/promotion、待激活工作、agent-ready Issue 和 roadmap 拆解均为空时才允许执行。被正常开发阻塞的到期扫描会保持 pending，等下一个真正空闲 tick 再运行。

Fixes #219