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)

Cargo.toml

@@ -54,6 +54,7 @@ async_zip = { version = "0.0.18", features = ["tokio", "deflate"] }
 dashmap = "6"
 socket2 = { version = "0.6.2", features = ["all"] }
 urlencoding = "2.1.3"
+utoipa = { version = "5", features = ["axum_extras", "uuid", "chrono"] }
 
 [features]
 default = []
@@ -63,6 +64,10 @@ integration_tests = []
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(integration_tests)'] }
 
+[[bin]]
+name = "generate-openapi"
+path = "src/bin/generate-openapi.rs"
+
 [build-dependencies]
 oxc_allocator = "0.116"
 oxc_parser = "0.116"