Add export/backup MCP tool

[arreyder]

Problem

No way to export or backup memories via the MCP interface. Had to fall back to direct Solr HTTP queries to create a backup.

Proposal

Add an export_memories MCP tool:

export_memories(
  agent_id: "dynamo-audit",  // optional filter
  tags: ["cost-optimization"], // optional filter
  format: "json",             // json or jsonl
)

Returns all matching memories as a JSON array, suitable for backup, migration, or import into another system.

Also consider an import_memories tool that accepts the same format for restore.

Workaround

Currently possible via direct Solr API: curl http://host:8983/solr/memories/select?q=*:*&rows=1000&wt=json