Add Dockerfile, docker-compose.yml, and coolify.json for deployment

SPA pattern: node build → nginx serve on port 3000, exposed via HOST_PORT.
Deploys to box-repoapps as spike-breakdown on port 2011, domain spikes.dotrepo.com.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

coolify.json

@@ -0,0 +1,9 @@
+{
+  "name": "spike-breakdown",
+  "buildpack": "dockercompose",
+  "branch": "master",
+  "port": 2011,
+  "domain": "spikes.dotrepo.com",
+  "server": "box-repoapps",
+  "repo": "idea.llm.spike.breakdown"
+}