style: cargo fmt across Phase 3.5 changes

Pure formatting pass — no behavior changes. Catches the line-wrapping
drift across the new authz / api_keys / middleware / handler edits
that piled up during the implementation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/auth.rs

@@ -223,6 +223,9 @@ mod tests {
         let b = generate_api_key().expect("mint b");
         assert_ne!(a.raw, b.raw);
         assert_ne!(a.hash, b.hash);
-        assert_ne!(a.prefix, b.prefix, "32 random bytes → prefix collision is negligible");
+        assert_ne!(
+            a.prefix, b.prefix,
+            "32 random bytes → prefix collision is negligible"
+        );
     }
 }