Enhance AI pipeline with credit guard integration and thinking trace support

- Added `thinkingCredits` to credit usage tracking.
- Implemented AI credit guard logic to handle blocked generation scenarios.
- Introduced logging for AI thinking traces, capturing reasoning and token usage.
- Updated tests to cover new credit guard behavior and thinking trace functionality.
- Adjusted generation result handling to accommodate new statuses and usage metrics.

Author: Rieranthony

apps/api/drizzle/migrations/0065_openrouter_byok_fallback_pause.sql

@@ -0,0 +1 @@
+ALTER TABLE "website_openrouter_key" ADD COLUMN "fallback_paused_until" timestamp;