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/failed_only_case_empty_oneliner_test.rs

@@ -14,12 +14,13 @@
 //! case to `Empty` through the same terminal branch used for silent-only
 //! cases.
 
+mod common;
+
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 
 use doctate_common::oneliners::OnelinerState;
-use doctate_server::config::Config;
 use doctate_server::events;
 use doctate_server::gazetteer::Gazetteer;
 use doctate_server::{
@@ -29,6 +30,8 @@ use tempfile::tempdir;
 use wiremock::matchers::{method, path as wm_path};
 use wiremock::{Mock, MockServer, ResponseTemplate};
 
+use common::TestConfig;
+
 #[tokio::test]
 async fn failed_only_case_settles_to_empty_without_llm_call() {
     let data = tempdir().unwrap();
@@ -50,10 +53,10 @@ async fn failed_only_case_settles_to_empty_without_llm_call() {
         .mount(&mock)
         .await;
 
-    let mut cfg = Config::test_default();
-    cfg.data_path = data.path().to_path_buf();
-    cfg.ollama_url = mock.uri();
-    let config = Arc::new(cfg);
+    let config = TestConfig::new()
+        .with_data_path(data.path().to_path_buf())
+        .with_ollama(mock.uri())
+        .build();
 
     let vocab = Arc::new(Gazetteer::empty());
     let events_tx = events::channel();