Add agent-coherence to Developer Tools

[hipvlady]

The LangGraph BaseStore docs say it "does not natively support optimistic locking, vector versioning, or invalidation protocols" and recommend strict reducer patterns. The Deep Agents async-subagent docs warn that "task statuses in conversation history are always stale." Reducer patterns handle plain concatenations. They don't catch the case where parallel nodes read the same key, reason, and write back snapshots that have diverged since the read.

CCSStore is a langgraph.store.BaseStore drop-in that adds MESI invalidation between holders of the same key. One import change, no node-code edits. Detects stale reads and lost writes at write time. Five sync strategies ship (eager, lazy, lease, access_count, broadcast).

Submitting under Developer Tools. 138-char description, under the 200-char CONTRIBUTING.md limit. Stars and last-commit badges per format.