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/openapi.rs

@@ -53,6 +53,11 @@ use utoipa::OpenApi;
         crate::metadata::get_metadata_links,
         crate::metadata::get_missing_books,
         crate::metadata::delete_metadata_link,
+        crate::books::series_statuses,
+        crate::books::provider_statuses,
+        crate::settings::list_status_mappings,
+        crate::settings::upsert_status_mapping,
+        crate::settings::delete_status_mapping,
     ),
     components(
         schemas(
@@ -93,6 +98,8 @@ use utoipa::OpenApi;
             crate::settings::ClearCacheResponse,
             crate::settings::CacheStats,
             crate::settings::ThumbnailStats,
+            crate::settings::StatusMappingDto,
+            crate::settings::UpsertStatusMappingRequest,
             crate::stats::StatsResponse,
             crate::stats::StatsOverview,
             crate::stats::ReadingStatusStats,
@@ -101,6 +108,8 @@ use utoipa::OpenApi;
             crate::stats::LibraryStats,
             crate::stats::TopSeries,
             crate::stats::MonthlyAdditions,
+            crate::stats::MetadataStats,
+            crate::stats::ProviderCount,
             crate::metadata::ApproveRequest,
             crate::metadata::ApproveResponse,
             crate::metadata::SyncReport,