feat: add Docker Compose deployment and serve assets via StaticFS

Embed full assets directory and serve with via's StaticFS instead of a
custom HTTP handler. Move SQLite DB to data/c4.db for clean volume
mounting. Add multi-stage Dockerfile, docker-compose.yml, and
.dockerignore.

.dockerignore

@@ -0,0 +1,10 @@
+c4
+c4.db
+data/
+deploy/
+.env
+.git
+.gitignore
+assets/css/output.css
+c4-deploy-*.tar.gz
+c4-deploy-*_b64*.txt