feat: add Cache TTL Override per account + bump VERSION to 0.1.83

- Account-level cache TTL override: rewrite Anthropic cache_creation
  token classification (5m↔1h) in streaming/non-streaming responses
- New DB field cache_ttl_overridden in usage_log for billing tracking
- Migration 055_add_cache_ttl_overridden
- Frontend: CacheTTL override toggle in account create/edit modals
- Ent schema regenerated for new usage_log fields

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

backend/migrations/055_add_cache_ttl_overridden.sql

@@ -0,0 +1,2 @@
+-- Add cache_ttl_overridden flag to usage_logs for tracking cache TTL override per account.
+ALTER TABLE usage_logs ADD COLUMN IF NOT EXISTS cache_ttl_overridden BOOLEAN NOT NULL DEFAULT FALSE;