SDK: surface type=recovery messages from CLI subprocess

[cpfiffer]

Context

When the Letta Code CLI (headless mode) detects a 409 PENDING_APPROVAL error, it autonomously attempts recovery by resolving pending approvals. During this process, it emits {"type": "recovery", ...} JSON messages to stdout.

The SDK's transformMessage() in session.ts does not handle type=recovery messages -- they are silently dropped. This means downstream consumers (like lettabot) have no visibility into what recovery the CLI attempted.

Impact

Currently low -- lettabot #478 added its own approval detection and recovery that works regardless of what the CLI does. However, surfacing recovery events would:

1. Improve debugging/observability when approval issues arise
2. Allow downstream consumers to avoid redundant recovery attempts
3. Give better visibility into the CLI's autonomous recovery behavior

Suggested fix

Add a type=recovery handler in transformMessage() (session.ts ~line 1083) that creates an SDKRecoveryMessage:

if (wireMsg.type === "recovery") {
  const msg = wireMsg as WireMessage & {
    recovery_type: string;
    message: string;
    session_id?: string;
  };
  return {
    type: "recovery" as const,
    recoveryType: msg.recovery_type,
    message: msg.message,
  };
}

Related: lettabot #478 (bot-side fix for #439/#438)