fix(tests): 更新 NVIDIA rate limiter 測試至當前配置值

ai_rate_limiter.py 在 2026-03-31 更新了 NVIDIA 免費版限制值，
但測試未同步更新導致失敗:
- rpm: 5 → 10 (放寬並發控制)
- daily_requests: 100 → 99999 (免費版無限制)
- daily_tokens: 50_000 → 9999999 (免費版無限制)
- total_cost_usd: 0.0 → 999999.0 (修復 $0>=0 永遠 True bug)

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

apps/api/tests/test_nvidia_provider.py

@@ -460,16 +460,16 @@ class TestRateLimiterIntegration:
         from src.services.ai_rate_limiter import RATE_LIMITS
 
         nvidia_limits = RATE_LIMITS["nvidia"]
-        assert nvidia_limits["rpm"] == 5  # 5 requests per minute
-        assert nvidia_limits["daily_requests"] == 100
-        assert nvidia_limits["daily_tokens"] == 50_000
+        assert nvidia_limits["rpm"] == 10  # 2026-04-01 ogt: 放寬到 10 (原 5)
+        assert nvidia_limits["daily_requests"] == 99999  # 免費版無限制，設大數 (原 100)
+        assert nvidia_limits["daily_tokens"] == 9999999  # 免費版無限制 (原 50_000)
 
     def test_nvidia_in_cost_limits(self):
         """測試 NVIDIA 在成本限制中 (免費 tier)"""
         from src.services.ai_rate_limiter import COST_LIMITS
 
         assert "nvidia" in COST_LIMITS
-        assert COST_LIMITS["nvidia"]["total_cost_usd"] == 0.0  # 免費
+        assert COST_LIMITS["nvidia"]["total_cost_usd"] == 999999.0  # 免費 Tier 無成本限制 (2026-04-01 ogt: 原 0.0)
 
 
 class TestCircuitBreaker: