feat: add MQTT journal server for session persistence

Implement a journal server that uses an Aedes MQTT broker to
persist stream messages to JSONL files and manage session metadata
via a manifest.

- Add `aedes`, `mqtt`, and `zod` dependencies
- Implement `createJournalServer` in `src/cli/journal.ts`
- Integrate journal server into the `serve` command
- Add `--mqtt-port` option to the CLI
- Add session lifecycle management (create, update, delete) via
  retained MQTT topics

src/cli/types.ts

@@ -1,14 +1,21 @@
 export interface ServeOptions {
   port: string;
   host?: string;
+  mqttPort?: string;
 }
 
 export interface CompileOptions {
   output: string;
 }
 
-export type ServeCommandHandler = (dir: string, options: ServeOptions) => Promise<void>;
-export type CompileCommandHandler = (dir: string, options: CompileOptions) => Promise<void>;
+export type ServeCommandHandler = (
+  dir: string,
+  options: ServeOptions,
+) => Promise<void>;
+export type CompileCommandHandler = (
+  dir: string,
+  options: CompileOptions,
+) => Promise<void>;
 
 export interface MarkdownFile {
   path: string;