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_providers/anilist.rs

@@ -128,7 +128,7 @@ async fn search_series_impl(
     let mut candidates: Vec<SeriesCandidate> = media
         .iter()
         .filter_map(|m| {
-            let id = m.get("id").and_then(|id| id.as_i64())? as i64;
+            let id = m.get("id").and_then(|id| id.as_i64())?;
             let title_obj = m.get("title")?;
             let title = title_obj
                 .get("english")