fix: normalize series status casing to avoid duplicates

- LOWER() all series_metadata.status values in the statuses endpoint
  to prevent "One shot" / "one shot" appearing as separate targets
- Migration 0040: lowercase all existing status values in DB
- Use LOWER() in series status filter queries for consistency

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

infra/migrations/0040_lowercase_series_status.sql

@@ -0,0 +1,5 @@
+-- Normalize all series_metadata.status values to lowercase for consistency.
+-- This fixes case mismatches like "One shot" vs "one shot".
+UPDATE series_metadata
+SET status = LOWER(status), updated_at = NOW()
+WHERE status IS NOT NULL AND status != LOWER(status);