fix(welfare): review 修复 — 里程碑"暂不发金币"文档同步 + 消息提醒奖励降为 1000

- comparison_milestone: 删 record_milestone_reward 死导入(ruff F401), 模块 docstring 同步"暂不发金币"
- 里程碑文档群对齐实现: compare-milestones / comparison_milestone_claim / MilestoneStateOut.coin 描述都标注暂不真发金币
- models/comparison: comparison_results JSONB 形状注释补 coupon_saved
- enable_notification 奖励 10000→1000(产品定, =¥0.1); test_exchange_flow 改 grant_coins 直接供款(不再靠该任务=兑换下限)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/models/comparison.py

@@ -83,7 +83,7 @@ class ComparisonRecord(Base):
     # ===== 明细(JSON,越详细越好)=====
     # 下单菜品 [{name, qty, specs?}]
     items: Mapped[list] = mapped_column(_JSON, nullable=False, default=list)
-    # 逐平台对比 [{platform_id, platform_name, package, price, is_source, rank}](price 单位:元,原样存)
+    # 逐平台对比 [{platform_id, platform_name, package, price, is_source, rank, coupon_saved}](price/coupon_saved 单位:元,原样存)
     comparison_results: Mapped[list] = mapped_column(_JSON, nullable=False, default=list)
     # 目标平台未找到、跳过的菜名
     skipped_dish_names: Mapped[list] = mapped_column(_JSON, nullable=False, default=list)