Association storage flips Table→Column when describe output is re-run; diff reports no change

[ako]

Plan item 0.4 in PROPOSAL_mdl_beta_syntax_freeze.md §8.1.

Symptom

• On a Studio Pro-authored association with table storage, describe association omits the storage clause.
• Running that output unchanged defaults the association to column storage. That changes the runtime database schema.
• mxcli diff reports "(no changes)" for it.

Reproduction

PedApp, Administration.AccountPasswordData_Account: before the round trip describe shows no storage clause; after it, storage column.

Fix

• describe always emits a storage value that round-trips.
• create or modify on an existing association keeps the stored storage when the statement does not state it (mdl/executor/cmd_associations.go).
• Find out why diff did not report the change.

Follow /mxcli-dev:fix-issue. Write the test first, prove the fix by reverting it, and record a finding.