refactor: 清理无用模块、修复前后端对齐、添加注册页面

- 删除后端 risk_exceptions 模块（API/Model/Schema/迁移/测试）
- 删除后端 metrics 模块（API/测试）
- 删除后端 ManualTask 模型和相关 Schema
- 修复搜索接口响应缺少 total 字段的问题
- 统一 Platform 枚举（前端去掉后端不支持的 weibo/wechat）
- 新增前端注册页面 /register，登录页添加注册链接

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/alembic/versions/001_initial_tables.py

@@ -32,18 +32,6 @@ def upgrade() -> None:
     )
     task_status_enum.create(op.get_bind(), checkfirst=True)
 
-    risk_target_type_enum = postgresql.ENUM(
-        'influencer', 'order', 'content',
-        name='risk_target_type_enum'
-    )
-    risk_target_type_enum.create(op.get_bind(), checkfirst=True)
-
-    risk_exception_status_enum = postgresql.ENUM(
-        'pending', 'approved', 'rejected', 'expired', 'revoked',
-        name='risk_exception_status_enum'
-    )
-    risk_exception_status_enum.create(op.get_bind(), checkfirst=True)
-
     # 租户表
     op.create_table(
         'tenants',
@@ -101,29 +89,6 @@ def upgrade() -> None:
     op.create_index('ix_review_tasks_creator_id', 'review_tasks', ['creator_id'])
     op.create_index('ix_review_tasks_status', 'review_tasks', ['status'])
 
-    # 人工任务表
-    op.create_table(
-        'manual_tasks',
-        sa.Column('id', sa.String(64), primary_key=True),
-        sa.Column('tenant_id', sa.String(64), sa.ForeignKey('tenants.id', ondelete='CASCADE'), nullable=False),
-        sa.Column('review_task_id', sa.String(64), sa.ForeignKey('review_tasks.id', ondelete='SET NULL'), nullable=True),
-        sa.Column('video_url', sa.String(2048), nullable=False),
-        sa.Column('platform', platform_enum, nullable=False),
-        sa.Column('creator_id', sa.String(64), nullable=False),
-        sa.Column('status', task_status_enum, nullable=False, default='pending'),
-        sa.Column('approve_comment', sa.Text(), nullable=True),
-        sa.Column('reject_reason', sa.Text(), nullable=True),
-        sa.Column('reject_violations', postgresql.JSONB(), nullable=True),
-        sa.Column('reviewer_id', sa.String(64), nullable=True),
-        sa.Column('reviewed_at', sa.DateTime(timezone=True), nullable=True),
-        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
-        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.func.now(), onupdate=sa.func.now(), nullable=False),
-    )
-    op.create_index('ix_manual_tasks_tenant_id', 'manual_tasks', ['tenant_id'])
-    op.create_index('ix_manual_tasks_review_task_id', 'manual_tasks', ['review_task_id'])
-    op.create_index('ix_manual_tasks_creator_id', 'manual_tasks', ['creator_id'])
-    op.create_index('ix_manual_tasks_status', 'manual_tasks', ['status'])
-
     # 违禁词表
     op.create_table(
         'forbidden_words',
@@ -169,49 +134,17 @@ def upgrade() -> None:
     op.create_index('ix_competitors_tenant_id', 'competitors', ['tenant_id'])
     op.create_index('ix_competitors_brand_id', 'competitors', ['brand_id'])
 
-    # 特例审批表
-    op.create_table(
-        'risk_exceptions',
-        sa.Column('id', sa.String(64), primary_key=True),
-        sa.Column('tenant_id', sa.String(64), sa.ForeignKey('tenants.id', ondelete='CASCADE'), nullable=False),
-        sa.Column('applicant_id', sa.String(64), nullable=False),
-        sa.Column('apply_time', sa.DateTime(timezone=True), nullable=False),
-        sa.Column('target_type', risk_target_type_enum, nullable=False),
-        sa.Column('target_id', sa.String(64), nullable=False),
-        sa.Column('risk_rule_id', sa.String(64), nullable=False),
-        sa.Column('status', risk_exception_status_enum, nullable=False, default='pending'),
-        sa.Column('valid_start_time', sa.DateTime(timezone=True), nullable=False),
-        sa.Column('valid_end_time', sa.DateTime(timezone=True), nullable=False),
-        sa.Column('reason_category', sa.String(100), nullable=False),
-        sa.Column('justification', sa.Text(), nullable=False),
-        sa.Column('attachment_url', sa.String(2048), nullable=True),
-        sa.Column('current_approver_id', sa.String(64), nullable=True),
-        sa.Column('approval_chain_log', postgresql.JSONB(), nullable=False, server_default='[]'),
-        sa.Column('auto_rejected', sa.Boolean(), nullable=False, default=False),
-        sa.Column('rejection_reason', sa.Text(), nullable=True),
-        sa.Column('last_status_at', sa.DateTime(timezone=True), nullable=True),
-        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
-        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.func.now(), onupdate=sa.func.now(), nullable=False),
-    )
-    op.create_index('ix_risk_exceptions_tenant_id', 'risk_exceptions', ['tenant_id'])
-    op.create_index('ix_risk_exceptions_applicant_id', 'risk_exceptions', ['applicant_id'])
-    op.create_index('ix_risk_exceptions_target_id', 'risk_exceptions', ['target_id'])
-    op.create_index('ix_risk_exceptions_status', 'risk_exceptions', ['status'])
 
 
 def downgrade() -> None:
     # 删除表
-    op.drop_table('risk_exceptions')
     op.drop_table('competitors')
     op.drop_table('whitelist_items')
     op.drop_table('forbidden_words')
-    op.drop_table('manual_tasks')
     op.drop_table('review_tasks')
     op.drop_table('ai_configs')
     op.drop_table('tenants')
 
     # 删除枚举类型
-    op.execute('DROP TYPE IF EXISTS risk_exception_status_enum')
-    op.execute('DROP TYPE IF EXISTS risk_target_type_enum')
     op.execute('DROP TYPE IF EXISTS task_status_enum')
     op.execute('DROP TYPE IF EXISTS platform_enum')