feat: add Docker deployment and application configuration

Add package declarations across the Go scaffold, YAML configuration loading and validation, and a minimal API entry point.

Add development and production Compose files, a multi-stage Docker image, configuration template, and Make targets. Remove the directory scaffolding script.

configs/config.example.yaml

@@ -0,0 +1,8 @@
+environment: development
+
+http:
+  address: 0.0.0.0:8080
+
+# The database is managed outside Docker Compose.
+database:
+  url: postgres://robot_market:change-me@host.docker.internal:5432/robot_market?sslmode=disable