Function createRatchetMessagesBackend

createRatchetMessagesBackend(options: RatchetMessagingOptions): MessagingBackend
A MessagingBackend for ratchet sessions (nostr-double-ratchet), over the active account's signer.

For each signed-in account the backend runs one NdrRuntime. The account signer signs the owner's device list; the library generates and holds its own device key and per-session ratchet keys, which never leave it except as ciphertext sealed to the account by createSealedRatchetStorage. Opening a runtime registers this browser as a device of the account and publishes its invite, so a correspondent can start a session; sessions and keys survive a reload, the conversation list does not (D-016).

Only chat messages are filed: typing notices, receipts and controls are dropped. Sessions are one to one, so a send names exactly one other person. When the account changes or signs out the runtime closes and the conversations are cleared.
Parameters
- options: RatchetMessagingOptions
  Pool, tiers, storage and the active account's signer and public key.
Returns MessagingBackend
A backend for the ratchet provider; available while the signer has nip44.
Example
```
const backend = createRatchetMessagesBackend({
  pool: kernl.pool,
  tiers: kernl.relays,
  storage: localStorage,
  signer: () => kernl.accounts.active,
  selfPubkey: () => kernl.accounts.active?.pubkey,
});
await backend.send({ recipients: [alice], content: 'hello' });
```