refactor(predict): migrate PredictController from Engine.context to messenger pattern

Replace all Engine.context usages with messenger.call() for proper controller
architecture alignment:

- KeyringController: signTypedMessage, signPersonalMessage
- NetworkController: findNetworkClientIdByChainId, getNetworkClientById
- RemoteFeatureFlagController: getState
- AccountTreeController: getAccountsFromSelectedAccountGroup

Update messenger factory delegation and test mocks accordingly.
All 213 tests passing.

Author: matallui