Add Dockerfile-based Dokku deployment for monorepo layout

Uses a multi-stage Docker build that copies both app/ and blogex/,
preserving the path dependency. Includes release scripts, migration
module, and a sample Dokku setup script.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app.json

@@ -0,0 +1,8 @@
+{
+  "name": "firehose",
+  "scripts": {
+    "dokku": {
+      "postdeploy": "/app/bin/migrate"
+    }
+  }
+}