fix(api): 修復 34 個 Ruff lint 錯誤

- 自動修復 import 排序、unused imports
- 手動修復 raise from、isinstance union、unused variable
- scripts/ 暫時保留 (非 CI 阻擋)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/services/nvidia_provider.py

@@ -34,7 +34,6 @@ from src.core.telemetry import get_tracer  # 2026-03-29 ogt: P1-2 OTEL 追蹤
 from src.models.nvidia import (
     NvidiaProviderResult,
     NvidiaResponse,
-    NvidiaUsage,
     ToolCallValidationResult,
     ToolDefinition,
 )