test(runtime): verify saveGraph ledger classification and execution order

[philipgreat]

Background

The current TeaQLRuntimeTest.testSaveGraph only verifies that a mutation executor was called. executeLedgerPlan now performs ordered delete, insert, and update work that is otherwise unprotected.

Scope

Add a recording MutationExecutor and metadata fixtures that verify ledger planning without a database. Related-entity root merging is tracked separately.

Test cases

• Deleted keys produce DELETE mutation requests.
• New keys with changes produce SAVE requests for newly created entities.
• Existing keys with changes produce update-style SAVE requests.
• A key marked deleted is not also inserted or updated.
• Deletes execute before inserts, and inserts before updates.
• Entity types and keys are processed deterministically.
• Root comments are propagated to mutation entities.
• The current change set is cleared after a successful save.

Acceptance criteria

• Assertions inspect recorded mutation requests, not private methods.
• The test uses in-memory stubs only.
• Existing smoke tests remain intact or are strengthened rather than duplicated.