feat: add configurable status mappings for metadata providers

Add a status_mappings table to replace hardcoded provider status
normalization. Users can now configure how provider statuses (e.g.
"releasing", "finie") map to target statuses (e.g. "ongoing", "ended")
via the Settings > Integrations page.

- Migration 0038: status_mappings table with pre-seeded mappings
- Migration 0039: re-normalize existing series_metadata.status values
- API: CRUD endpoints for status mappings, DB-based normalize function
- API: new GET /series/provider-statuses endpoint
- Backoffice: StatusMappingsCard component with create target, assign,
  and delete capabilities
- Fix all clippy warnings across the API crate
- Fix missing OpenAPI schema refs (MetadataStats, ProviderCount)

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

apps/api/src/metadata_refresh.rs

@@ -574,9 +574,12 @@ async fn sync_series_with_diff(
     let new_publishers = &candidate.publishers;
     let new_start_year = candidate.start_year;
     let new_total_volumes = candidate.total_volumes;
-    let new_status = candidate.metadata_json
-        .get("status")
-        .and_then(|s| s.as_str());
+    let new_status = if let Some(raw) = candidate.metadata_json.get("status").and_then(|s| s.as_str()) {
+        Some(crate::metadata::normalize_series_status(pool, raw).await)
+    } else {
+        None
+    };
+    let new_status = new_status.as_deref();
 
     // Fetch existing series metadata for diffing
     let existing = sqlx::query(