fix(mongo): JSON filter cannot match ObjectId / DateTime fields

[ZhuchkaTriplesix]

Summary

Document list filter is json.decode into a map passed to find. {\"_id\": \"<hex>\"} and ISO date strings do not match BSON ObjectId / DateTime, so the filter returns empty with no hint. Same type-loss family as the document editor.

Scope

• Accept Extended JSON in the filter box ({\"_id\": {\"\$oid\": \"…\"}}) or detect a 24-char hex _id and wrap ObjectId.
• Empty-result hint when the filter looks like an _id string.
• Tests for ObjectId equality in find filter construction.

Out of scope

• Full aggregation pipeline UI.

[ZhuchkaTriplesix]

Shipped in #861