feat(coordination): 增加 durable Session 输出桥接

[zsnjuts]

依赖

基于 #1706 继续堆叠；本切片 commit 79ab4d18e。

改动

• 先 exact-write 最新完整 Session snapshot，取得新 lease/record。
• 用同一 fencing epoch enqueue frozen outbox message。
• 返回可跨副本 takeover 的 authoritative settlement，供 final-drain 等待。
• outbox Session key 在任何写入前校验；Session occupied 与 outbox conflict/stale 均 fail closed。
• 仍未接 daemon，primary 保持禁用。

验证

• TypeScript 通过
• Node 14/14
• Bun 1.4.2 14/14
• public-domain audit 通过

[zsnjuts]

Superseded by milestone PR #1710. This commit slice is retained in that branch; closing the cumulative intermediate Draft to keep the review stack to five milestones.

[zsnjuts]

Superseded by milestone PR #1710. This commit slice is retained in that branch; closing the cumulative intermediate Draft to keep the review stack to five milestones.