[Phase 3.1] Add team collaboration rules configuration

[loonghao]

Parent Issue

Part of #273 - .vx.toml v2 Configuration Enhancement

Objective

Add team collaboration rules for code ownership, review policies, and conventions.

Configuration Format

[team]
extends = "https://github.com/org/vx-presets/base.toml"

[team.code_owners]
"src/api/**" = ["@backend-team"]
"src/ui/**" = ["@frontend-team"]
"*.md" = ["@docs-team"]

[team.review]
required_approvals = 2
auto_assign = true
dismiss_stale = true

[team.conventions]
commit_format = "conventional"  # conventional | angular | custom
branch_pattern = "^(feature|fix|docs|refactor)/[a-z0-9-]+$"
pr_template = ".github/pull_request_template.md"

Tasks

• Define TeamConfig structure
• Implement config inheritance (extends)
• Generate CODEOWNERS file from config
• Add commit message validation
• Add branch name validation
• Implement vx team check command
• Add unit tests

Commands

vx team check              # Validate team conventions
vx team export codeowners  # Generate CODEOWNERS
vx team export pr-template # Generate PR template

Acceptance Criteria

• Config inheritance works
• CODEOWNERS generated correctly
• Commit format validated
• Branch naming validated