feat: add OpenAPI spec generation with utoipa and justfile

- Add utoipa v5 dependency with ToSchema derives on all REST API DTOs
- Annotate free-function handlers with #[utoipa::path] (trash, share, favorites, recent)
- Create ApiDoc struct with OpenApi derive registering 37 schemas across 7 tags
- Add generate-openapi binary outputting resources/gen/openapi.json
- Serve OpenAPI spec at GET /api/openapi.json (public, no auth)
- Add justfile with common dev commands (build, test, lint, check, openapi, db)

src/bin/generate-openapi.rs

@@ -0,0 +1,24 @@
+use oxicloud::interfaces::api::ApiDoc;
+use std::fs;
+use std::path::PathBuf;
+use utoipa::OpenApi;
+
+fn main() {
+    let openapi = ApiDoc::openapi();
+
+    let json =
+        serde_json::to_string_pretty(&openapi).expect("Failed to serialize OpenAPI spec to JSON");
+
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+
+    let resources_gen_dir = manifest_dir.join("resources").join("gen");
+    fs::create_dir_all(&resources_gen_dir).expect("Failed to create resources/gen directory");
+
+    let output_path = resources_gen_dir.join("openapi.json");
+    fs::write(&output_path, json).expect("Failed to write OpenAPI spec to file");
+
+    println!(
+        "OpenAPI spec generated successfully at: {}",
+        output_path.display()
+    );
+}