fix(imessage): unify timeout configuration with configurable probeTimeoutMs

- Add probeTimeoutMs config option to channels.imessage
- Export DEFAULT_IMESSAGE_PROBE_TIMEOUT_MS constant (10s) from probe.ts
- Propagate timeout config through all iMessage probe/RPC operations
- Fix hardcoded 2000ms timeouts that were too short for SSH connections

Closes: timeout issues when using SSH wrapper scripts (imsg-ssh)

src/config/types.imessage.ts

@@ -52,6 +52,8 @@ export type IMessageAccountConfig = {
   includeAttachments?: boolean;
   /** Max outbound media size in MB. */
   mediaMaxMb?: number;
+  /** Timeout for probe/RPC operations in milliseconds (default: 10000). */
+  probeTimeoutMs?: number;
   /** Outbound text chunk size (chars). Default: 4000. */
   textChunkLimit?: number;
   /** Chunking mode: "length" (default) splits by size; "newline" splits on every newline. */