feat(internal): 启动确认窗 agent 兜底样本落盘(pricebot 回写)

- 新增内部端点 POST /internal/launch-confirm-sample(X-Internal-Secret 鉴权):
  pricebot 对没见过文案的启动确认窗用 LLM 兜底放行后,把样本(host 包 / 弹窗树 /
  LLM plan / 设备 locale 机型)回写落 launch_confirm_sample 表,供研发人工沉淀回
  pricebot 规则 yaml
- 配套: model LaunchConfirmSample + schema + repo(都上报不去重) + alembic 迁移
  launch_confirm_sample_table(down_revision=cps_wx_user) + main 注册 router +
  models/__init__ 登记
- docs: 后端技术实现.md 加 §6.5 pricebot 回写内部端点说明

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/models/__init__.py

@@ -20,6 +20,7 @@ from app.models.coupon_state import (  # noqa: F401
 from app.models.feedback import Feedback  # noqa: F401
 from app.models.invite import InviteRelation  # noqa: F401
 from app.models.invite_fingerprint import InviteFingerprint  # noqa: F401
+from app.models.launch_confirm_sample import LaunchConfirmSample  # noqa: F401
 from app.models.meituan_coupon import MeituanCoupon  # noqa: F401
 from app.models.onboarding import OnboardingCompletion  # noqa: F401
 from app.models.ops_marquee_seed import OpsMarqueeSeed  # noqa: F401