feat(db): support $unset operator in update operations

[gowthamrdyy]

Summary

Adds support for the $unset operator in the update() method of db-client.ts, allowing callers to remove specific fields from a document without replacing the entire object.

Contributing on behalf of GSSoC'26 🚀

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Problem

Currently, ZerithDB's update() only supports field-value replacement via $set. There is no way to remove a field from a stored document. This is a common requirement — e.g., clearing a user's refreshToken or removing an optional metadata field.

Solution

• Extended the UpdateFilter<T> type to accept an optional $unset key whose value is a Partial<Record<keyof T, 1>> (mirroring the MongoDB $unset convention).
• In update(), after applying $set mutations, any keys present in $unset are deleted from the document object before the final dexie.table.put() call.
• Added a changeset entry under .changeset/.

Files Changed

File	Change
packages/db/src/db-client.ts	Implemented $unset handling in update()
tests/unit/db.test.ts	Added unit test: verify field is removed after $unset
.changeset/support-unset-operator.md	Changeset for minor release

Test

pnpm vitest run tests/unit/db.test.ts

All existing tests pass; the new $unset test case verifies the field is correctly removed.

Checklist

• Follows existing code style
• Unit tests added and passing
• Changeset file included
• No breaking changes (purely additive)