Convert the credentials store to Query

[ExtraToast]

What to build

The credentials store's server state moves into the query cache, and the store is removed.

Reads become queries keyed from the contract, writes become mutations that invalidate the keys they affect, and the loading and error flags the store hand-maintained come from the query itself. This store holds the most sensitive data in the application, so pay particular attention to what the cache retains after sign-out.

Acceptance criteria

• The screens backed by this store read from the query cache
• A write updates every affected screen without a manual refresh
• Client errors are not retried, and failures render through the estate's existing error path
• The store no longer exists, and coverage thresholds still pass after its tests are removed with it

Blocked by

• Migrate projects, repositories, credentials and account to the generated SDK