feat(init): 完成 Phase 1 基础架构搭建

- 完成 T-001A: 前端项目初始化 (Next.js 14 + TypeScript + Tailwind CSS)
- 完成 T-001B: 后端项目初始化 (FastAPI + SQLAlchemy + asyncpg)
- 完成 T-002: 数据库配置 (KolVideo 模型 + 索引 + 测试)
- 完成 T-003: 基础 UI 框架 (Header/Footer 组件 + 品牌色系)
- 完成 T-004: 环境变量配置 (前后端环境变量)

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

backend/app/models/__init__.py

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+from app.models.kol_video import KolVideo
+
+__all__ = ["KolVideo"]

backend/app/models/kol_video.py

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+from sqlalchemy import Column, String, Integer, Float, DateTime, Index
+from app.database import Base
+
+
+class KolVideo(Base):
+    """KOL 视频数据模型."""
+
+    __tablename__ = "kol_videos"
+
+    # 主键
+    item_id = Column(String, primary_key=True)
+
+    # 基础信息
+    title = Column(String, nullable=True)
+    viral_type = Column(String, nullable=True)
+    video_url = Column(String, nullable=True)
+    star_id = Column(String, nullable=False)
+    star_unique_id = Column(String, nullable=False)
+    star_nickname = Column(String, nullable=False)
+    publish_time = Column(DateTime, nullable=True)
+
+    # 曝光指标
+    natural_play_cnt = Column(Integer, default=0)
+    heated_play_cnt = Column(Integer, default=0)
+    total_play_cnt = Column(Integer, default=0)
+
+    # 互动指标
+    total_interact = Column(Integer, default=0)
+    like_cnt = Column(Integer, default=0)
+    share_cnt = Column(Integer, default=0)
+    comment_cnt = Column(Integer, default=0)
+
+    # 效果指标
+    new_a3_rate = Column(Float, nullable=True)
+    after_view_search_uv = Column(Integer, default=0)
+    return_search_cnt = Column(Integer, default=0)
+
+    # 商业信息
+    industry_id = Column(String, nullable=True)
+    industry_name = Column(String, nullable=True)
+    brand_id = Column(String, nullable=True)
+    estimated_video_cost = Column(Float, default=0)
+
+    # 索引定义
+    __table_args__ = (
+        Index("idx_star_id", "star_id"),
+        Index("idx_star_unique_id", "star_unique_id"),
+        Index("idx_star_nickname", "star_nickname"),
+    )
+
+    def __repr__(self):
+        return f"<KolVideo(item_id={self.item_id}, title={self.title})>"