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/users.rs

@@ -58,11 +58,7 @@ pub fn test_user_with_password(slug: &str, password: &str) -> User {
 
 /// Doctor user with custom retention settings — for the retention sweep
 /// tests that drive the lazy auto-close / auto-purge logic.
-pub fn test_user_with_retention(
-    slug: &str,
-    auto_close_days: u32,
-    auto_delete_days: u32,
-) -> User {
+pub fn test_user_with_retention(slug: &str, auto_close_days: u32, auto_delete_days: u32) -> User {
     let mut u = test_user(slug);
     u.retention = RetentionUserSettings {
         auto_close_days,