fix: surface human thread replies to MCP agents

[alexgorbatchev]

Summary

• Fixed agentation_watch_annotations to detect thread.message SSE events from humans, not just annotation.created events. Agent replies are correctly filtered out so they don't trigger false wakeups.
• Added getAnnotationsNeedingAttention store method that returns both pending annotations AND non-pending annotations where the last thread message is from a human (unread reply). Updated the /pending HTTP endpoints and SSE initial sync to use this broader check.
• Added integration tests covering all thread reply visibility scenarios: acknowledged annotations with human replies, resolved annotations with human replies, agent-only replies not resurfacing, and SSE watcher detecting thread.message events.

Problem

When a human replied to an annotation thread, the agent could not see it because:

1. The SSE watcher only listened for annotation.created events, ignoring thread.message entirely
2. get_pending filtered by status='pending', so once acknowledged, any human reply was invisible

Test plan

• New test: human reply to acknowledged annotation is visible via get_pending
• New test: watch_annotations detects thread.message events from humans
• New test: thread messages are included in get_session response
• New test: multiple human replies all surface to the agent
• New test: agent reply does NOT re-surface annotation as needing attention
• New test: resolved annotation with human reply resurfaces for agent
• All 825 existing package tests pass (no regressions)
• MCP package builds successfully with no TypeScript errors

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