refactor(tests): migrate remaining batches to tests/common/

Finishes the lift of shared helpers into `tests/common/`. Covered:
- health, web, oneliners_api, upload (31 tests; upload exercises the
  new `multipart_upload_body` helper driven by doctate_common field
  constants)
- sse_integration, sse_cleanup, transcribe, oneliner_heal_decoupled,
  silent_case_empty, failed_only_case_empty_oneliner,
  transient_failure_retries (24 tests)

Also applied cargo fmt across the test tree and fixed one clippy
needless_borrows_for_generic_args warning in analyze_test.

All 387 tests pass; 3 ignored (as before).

Side effect: health_test previously used a hardcoded `/tmp/doctate-test`
data path, which parallel `cargo test` runs could collide on. The
migration replaces it with the common unique-tmpdir pattern, removing
a latent flake.

server/tests/csrf_attack_test.rs

@@ -292,7 +292,11 @@ async fn bulk_with_injection_payload_returns_403_not_500() {
 // the browser flow breaks and one of these fires.
 
 async fn html_body(app: &axum::Router, uri: &str, cookie: &str) -> String {
-    let resp = app.clone().oneshot(get_with_cookie(uri, cookie)).await.unwrap();
+    let resp = app
+        .clone()
+        .oneshot(get_with_cookie(uri, cookie))
+        .await
+        .unwrap();
     assert_eq!(resp.status(), StatusCode::OK, "GET {uri} failed");
     common::body_string(resp).await
 }