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>

infra/migrations/0039_renormalize_series_status.sql

@@ -0,0 +1,19 @@
+-- Re-normalize series_metadata.status using the status_mappings table.
+-- Batch sync was not calling normalize_series_status before, so raw provider
+-- values like "Série en cours" ended up in the DB alongside "ongoing".
+
+-- Exact match
+UPDATE series_metadata sm
+SET status = m.mapped_status, updated_at = NOW()
+FROM status_mappings m
+WHERE LOWER(sm.status) = m.provider_status
+  AND sm.status IS NOT NULL
+  AND LOWER(sm.status) != m.mapped_status;
+
+-- Substring match (for values like "Série en cours" containing "en cours")
+UPDATE series_metadata sm
+SET status = m.mapped_status, updated_at = NOW()
+FROM status_mappings m
+WHERE LOWER(sm.status) LIKE '%' || m.provider_status || '%'
+  AND sm.status IS NOT NULL
+  AND LOWER(sm.status) != m.mapped_status;