chore(security): 摘除 knowledge_service 硬编码默认 DeepSeek Key（缺 env 抛明确错误/503）

- knowledge_service: 移除 os.getenv 默认值占位，改 _require_deepseek_key() 必填，缺 env 抛 DeepSeekKeyMissing
- knowledge API: generate/{daily,weekly,monthly} 缺 Key 返回 503（可观测，不再静默走模板兜底）
- finance_bot / verify_zxt_vouchers_json / bot_bridge_push: 凭据改 env 优先（CMA_BOT_KEY_* / CMA_BOT_API_KEYS / CMA_BRIDGE_TOKEN），历史共享键仅作兼容期兜底并告警
- tests: 新增 5 例回归（缺 Key 服务层抛错、API 503；有 Key 正常 200）

(cherry picked from commit 859bd8276d7c5aad4bf10ee3399b6cccc188f064)

backend/app/api/knowledge.py

@@ -18,6 +18,7 @@ from app.auth_middleware import require_role
 from app.deps import get_entity_id
 from app.models import KnowledgeEvent, KnowledgeSummary
 from app.services.knowledge_service import (
+    DeepSeekKeyMissing,
     generate_summary_sync,
     generate_daily_sync,
     generate_weekly_sync,
@@ -150,6 +151,9 @@ def trigger_daily_summary(
     try:
         result = generate_daily_sync(db, entity_id=entity_id)
         return {"message": "每日摘要已生成", "summary": result}
+    except DeepSeekKeyMissing as e:
+        logger.error("每日摘要生成失败（缺少 DeepSeek Key）: %s", e)
+        raise HTTPException(status_code=503, detail=str(e))
     except Exception as e:
         logger.exception("每日摘要生成失败")
         raise HTTPException(status_code=500, detail=f"生成失败: {str(e)}")
@@ -164,6 +168,9 @@ def trigger_weekly_summary(
     try:
         result = generate_weekly_sync(db, entity_id=entity_id)
         return {"message": "周度摘要已生成", "summary": result}
+    except DeepSeekKeyMissing as e:
+        logger.error("周度摘要生成失败（缺少 DeepSeek Key）: %s", e)
+        raise HTTPException(status_code=503, detail=str(e))
     except Exception as e:
         logger.exception("周度摘要生成失败")
         raise HTTPException(status_code=500, detail=f"生成失败: {str(e)}")
@@ -178,6 +185,9 @@ def trigger_monthly_summary(
     try:
         result = generate_monthly_sync(db, entity_id=entity_id)
         return {"message": "月度摘要已生成", "summary": result}
+    except DeepSeekKeyMissing as e:
+        logger.error("月度摘要生成失败（缺少 DeepSeek Key）: %s", e)
+        raise HTTPException(status_code=503, detail=str(e))
     except Exception as e:
         logger.exception("月度摘要生成失败")
         raise HTTPException(status_code=500, detail=f"生成失败: {str(e)}")