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/common/http.rs

@@ -121,11 +121,7 @@ pub fn header_str(response: &Response, name: &str) -> String {
 /// Uses the server's canonical field names (`case_id`, `recorded_at`,
 /// `audio`) from `doctate_common::constants`, so a server-side rename
 /// propagates here for free.
-pub fn multipart_upload_body(
-    case_id: &str,
-    recorded_at: &str,
-    audio: &[u8],
-) -> (String, Vec<u8>) {
+pub fn multipart_upload_body(case_id: &str, recorded_at: &str, audio: &[u8]) -> (String, Vec<u8>) {
     let boundary = "----testboundary";
     let mut body = Vec::new();