fix(ai-gateway): reduce provider sync log spam

[chrarnoldus]

Summary

• Replace per-model gateway sync debug logs with one aggregate log per gateway.
• Preserve the fetched model count and gateway ID for successful sync observability without emitting hundreds of lines.

Verification

N/A - logging-only change with no user-facing behavior.

Visual Changes

N/A

Reviewer Notes

The aggregate debug log is emitted only after the existing minimum model-count validation succeeds.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• apps/web/src/lib/ai-gateway/providers/openrouter/sync-providers.ts

---

_{Reviewed by gpt-5.4-20260305 · Input: 32K · Output: 3.8K · Cached: 161.3K}

_{Review guidance: REVIEW.md from base branch main}