Function createDefaultMessaging

createDefaultMessaging(options: DefaultMessagingOptions): MessagingRegistry
The shell's messaging registry with kernl's four providers registered and preferences persisted at kernl:messaging:v1.

createKernl passes the account-signer backends for all four providers and the active account's signer, so each follows the account: sign-in-required while nobody is signed in, signer-cannot-encrypt while the signer lacks the encryption the format needs. A provider given no backend stays unavailable: no-runtime for ratchet and group, sign-in-required for the others. The shell describes, it does not pretend.

The providers start in the order private, legacy, ratchet, group, with private and legacy switched on for someone who has never chosen; each starts as soon as an account that can run it signs in. The user's own choices, order, reply rule and per-person answers are saved and win.
Parameters
- options: DefaultMessagingOptions
  Storage, backend constructors, the active signer and the reply question.
Returns MessagingRegistry
A MessagingRegistry.
Example
```
const messaging = createDefaultMessaging({ storage: localStorage });
messaging.get('private')?.availability; // { available: false, reason: 'sign-in-required' }
messaging.get('ratchet')?.availability; // { available: false, reason: 'no-runtime' }
messaging.get('group')?.availability; // { available: false, reason: 'no-runtime' }
```