Note

Low Risk
Doc-only changes (JSDoc @deprecated annotations and changelog entry) with no runtime behavior changes; risk is limited to consumers treating deprecations as warnings/errors in stricter builds.

Overview
Marks AccountsController as deprecated across the package by adding JSDoc @deprecated annotations to the class, EMPTY_ACCOUNT, exported action/event/state types, and key public methods (e.g., getAccount, listMultichainAccounts, updateAccounts, loadBackup).

Updates the accounts-controller changelog to announce the deprecation and point consumers to AccountTreeController, MultichainAccountService, and Keyring API v2.

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