Add OpenAPI/Swagger documentation

- Add Swagger dependencies to go.mod
- Annotate all API endpoints with Swagger comments
- Add Swagger UI at /api/v1/docs endpoint
- Auto-generate Swagger docs in Dockerfile build
- Update README with API documentation link

cmd/api/main.go

@@ -15,6 +15,25 @@ import (
 	"apocapoc-api/internal/infrastructure/persistence/sqlite"
 )
 
+// @title Apocapoc API
+// @version 1.0
+// @description Self-hosted habit tracking service
+// @termsOfService http://swagger.io/terms/
+
+// @contact.name API Support
+// @contact.url https://github.com/davidfolch/apocapoc-api
+
+// @license.name MIT
+// @license.url https://opensource.org/licenses/MIT
+
+// @host localhost:8080
+// @BasePath /api/v1
+
+// @securityDefinitions.apikey BearerAuth
+// @in header
+// @name Authorization
+// @description Type "Bearer" followed by a space and JWT token.
+
 func main() {
 	cfg, err := config.Load()
 	if err != nil {