feat(api): dockerize backend with compose, migrations-on-start, and run docs

docs/README.md

@@ -0,0 +1,20 @@
+# SoleLog docs
+
+- [Roadmap & project overview](./roadmap.md)
+- [Plans](./plans/)
+
+## Running the backend (Phase 0)
+
+Local (dev):
+```bash
+yarn install
+cp apps/api/.env.example apps/api/.env   # edit BETTER_AUTH_SECRET
+yarn workspace @solelog/api db:migrate
+yarn workspace @solelog/api dev
+```
+
+Docker (whole stack):
+```bash
+docker compose up --build
+# health: curl http://localhost:3000/health
+```