[Phase 2.2] Add documentation auto-generation

[loonghao]

Parent Issue

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

Objective

Add configuration for automatic documentation generation.

Configuration Format

[docs]
enabled = true
output = "docs/generated"

[docs.api]
generator = "typedoc"  # typedoc | sphinx | godoc | rustdoc
source = "src"
output = "docs/api"

[docs.changelog]
generator = "conventional-changelog"
preset = "angular"

[docs.readme]
badges = ["ci", "coverage", "version", "license"]
sections = ["installation", "usage", "api", "contributing"]

Tasks

• Define DocsConfig structure
• Implement vx docs generate command
• Add API documentation generation
• Add changelog generation from commits
• Add README badge/section updates
• Support multiple documentation generators
• Add unit tests

Commands

vx docs generate           # Generate all docs
vx docs api                # Generate API docs only
vx docs changelog          # Generate changelog
vx docs readme             # Update README

Acceptance Criteria

• API docs generated correctly
• Changelog follows conventional commits
• README badges are valid
• Multiple generators supported