feat: team config + role definitions (Phase 2 of Agent Teams)

[LeoLin990405]

Summary / 概述

Phase 2 of Agent Teams (#81): 添加 team 配置系统，支持命名 agent 及角色定义。
Adds team configuration with named agents, provider/model binding, roles, and skills.

依赖 / Depends on: #133 (Phase 1 agent aliases)

新文件 / New Files

• lib/team_config.py (129 行) — Team 配置加载、agent 解析、名称解析
• test/test_team_config.py (387 行) — 38 个测试覆盖所有路径

修改 / Modified

• bin/ask — 集成 team agent 解析，优先级：team agents > aliases > direct providers

使用方式 / Usage

创建 .ccb/team.json（项目级）或 ~/.ccb/team.json（全局）：
Create .ccb/team.json (project) or ~/.ccb/team.json (global):

{
  "name": "dev-team",
  "description": "开发团队 / Development team",
  "strategy": "skill_based",
  "agents": [
    {"name": "researcher", "provider": "gemini", "model": "3f", "role": "research", "skills": ["frontend", "analysis"]},
    {"name": "coder", "provider": "codex", "model": "o3", "role": "implementation", "skills": ["python", "rust"]},
    {"name": "reviewer", "provider": "claude", "role": "review", "skills": ["security", "architecture"]}
  ]
}

用 team agent 名称路由 / Route by team agent name:

ask researcher "分析这个前端架构"  # → gemini (3f)
ask coder "实现排序算法"          # → codex (o3)
ask reviewer "审查这段代码"       # → claude
ask a "hello"                    # → 别名仍有效 / aliases still work
ask kimi "hello"                 # → 直接 provider 不变 / direct unchanged

设计要点 / Design

特性	说明
解析优先级 / Resolution order	team agents > aliases > direct providers
配置层级 / Config layers	项目 .ccb/team.json 覆盖全局 ~/.ccb/team.json
Daemon 零改动 / Zero daemon changes	解析完全在 bin/ask 客户端
向后兼容 / Backward compatible	无 team 配置时行为完全不变
分配策略 / Strategies	round_robin / load_balance / skill_based（Phase 3 使用）
容错 / Fault tolerant	JSON 损坏、无效 agent、缺失字段均安全处理

Agent 字段 / Agent Fields

字段	必填	说明
name	✅	Agent 名称（大小写不敏感）
provider	✅	Provider 名称 (codex, gemini, claude, etc.)
model	❌	模型标识 (o3, 3f, thinking, etc.)，Phase 3 路由使用
role	❌	角色 (research, implementation, review, etc.)
skills	❌	技能标签数组，Phase 3 skill_based 路由使用

阶段路线图 / Phased Roadmap

Phase	内容 / Content	状态 / Status
1	Agent 别名 / Agent aliases	✅ #133
2	Team 配置 + 角色定义 / Team config + roles (this PR)	✅
3	任务分发 + 智能路由 / Task distribution + smart routing	Planned
4	Agent 间通信 / Inter-agent communication	Planned

Relates to #81

测试计划 / Test plan

• pytest test/test_team_config.py -v — 38/38 passed
• pytest test/test_aliases.py -v — 22/22 passed (Phase 1 不受影响)
• 全量回归 / Full regression — 86/86 passed (零回归)
• 手动测试：创建 .ccb/team.json，验证 ask researcher "hello" → gemini
• 手动测试：无 team 配置时别名和直接 provider 正常工作
• 手动测试：ask --help 显示 team 信息