fix: resolve all clippy warnings for CI (async_fn_in_trait, collapsible_if, type_complexity, dead_code)

- Allow async_fn_in_trait lint crate-wide (internal project, 413 warnings)
- Add integration_tests feature to Cargo.toml to fix unexpected cfg warnings
- Collapse nested if statements into single conditions (13 locations)
- Add type_complexity allows on pg repository functions (12 locations)
- Fix dead code warnings in test modules with allow attributes
- Fix E0599 by gating new_stub() for integration_tests feature
- Add result_unit_err and result_large_err allows where appropriate
- Apply rustfmt formatting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/interfaces/nextcloud/basic_auth_middleware.rs

@@ -63,15 +63,15 @@ pub async fn basic_auth_middleware(
         parse_basic_auth(auth_header).ok_or(NextcloudAuthError::Unauthorized)?;
 
     // Check account lockout before attempting password verification (saves CPU)
-    if let Some(auth_svc) = state.auth_service.as_ref() {
-        if let Err(secs) = auth_svc.login_lockout.check(&username) {
-            tracing::warn!(
-                username = %username,
-                lockout_remaining_secs = secs,
-                "[NC] Account locked — too many failed attempts"
-            );
-            return Err(NextcloudAuthError::Unauthorized);
-        }
+    if let Some(auth_svc) = state.auth_service.as_ref()
+        && let Err(secs) = auth_svc.login_lockout.check(&username)
+    {
+        tracing::warn!(
+            username = %username,
+            lockout_remaining_secs = secs,
+            "[NC] Account locked — too many failed attempts"
+        );
+        return Err(NextcloudAuthError::Unauthorized);
     }
 
     let nextcloud = state