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/0038_add_status_mappings.sql

@@ -0,0 +1,24 @@
+-- Status mappings: many provider statuses → one target status (existing in series_metadata.status)
+CREATE TABLE status_mappings (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    provider_status TEXT NOT NULL UNIQUE,
+    mapped_status TEXT NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Pre-populate with current hardcoded mappings from normalize_series_status
+INSERT INTO status_mappings (provider_status, mapped_status) VALUES
+    -- AniList
+    ('finished', 'ended'),
+    ('releasing', 'ongoing'),
+    ('not_yet_released', 'upcoming'),
+    ('cancelled', 'cancelled'),
+    ('hiatus', 'hiatus'),
+    -- Bédéthèque (French)
+    ('finie', 'ended'),
+    ('terminée', 'ended'),
+    ('en cours', 'ongoing'),
+    ('suspendue', 'hiatus'),
+    ('annulée', 'cancelled'),
+    ('arrêtée', 'cancelled');