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

package.json

@@ -36,6 +36,7 @@
     "@solidjs/router": "^0.15.0",
     "@thisbeyond/solid-dnd": "^0.7.5",
     "@types/three": "^0.183.1",
+    "aedes": "^1.1.1",
     "chokidar": "^5.0.0",
     "commander": "^14.0.3",
     "csv-parse": "^6.1.0",
@@ -46,11 +47,13 @@
     "marked-directive": "^1.0.7",
     "marked-gfm-heading-id": "^4.1.3",
     "mermaid": "^11.0.0",
+    "mqtt": "^5.15.1",
     "solid-element": "^1.9.1",
     "solid-js": "^1.9.3",
     "three": "^0.183.2",
     "three-3mf-exporter": "^45.1.0",
-    "yarn-spinner-loader": "^0.1.0"
+    "yarn-spinner-loader": "^0.1.0",
+    "zod": "^4.4.3"
   },
   "devDependencies": {
     "@image-tracer-ts/core": "^1.0.2",