feat: add OpenAPI spec (dev only) with typed frontend client

- Add springdoc-openapi 3.0.2 (supports Spring Boot 4) to backend
- Disable api-docs/swagger-ui in application.yaml (prod default)
- Enable both in application-dev.yaml; Swagger UI at /swagger-ui.html
- Add openapi-fetch (runtime) and openapi-typescript (dev) to frontend
- Add generate:api npm script — run with backend up to regenerate types
- Add src/lib/api.server.ts typed client factory (uses SvelteKit fetch)
- Gitignore src/lib/generated/api.ts (generated artifact)

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

backend/pom.xml

@@ -136,6 +136,13 @@
 			<groupId>org.flywaydb</groupId>
 			<artifactId>flyway-database-postgresql</artifactId>
 		</dependency>
+
+		<!-- OpenAPI / Swagger UI — enabled only in the dev Spring profile -->
+		<dependency>
+			<groupId>org.springdoc</groupId>
+			<artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
+			<version>3.0.2</version>
+		</dependency>
 	</dependencies>