fix(mongo): silent 0-match updateOne looks like a successful save

[ZhuchkaTriplesix]

Summary

MongoService.updateDocument awaits coll.updateOne(filter, update) and returns void. mongo_dart does not throw when nMatched == 0 (wrong _id type, deleted doc, replica lag). Inspector then _load()s and the field looks unchanged with no error.

Same class of lie as 0-row SQL DML.

Scope

• Inspect WriteResult / nMatched / nModified after updateOne and deleteOne.
• Throw (or return a result) when filter matched 0 documents.
• Surface in inspector / full-doc editor as Save Failed.

Out of scope

• Retry / conflict UI.

[ZhuchkaTriplesix]

Shipped in #864