Add monorepo/workspace support

[endavis]

Problem

Template only supports single-package projects. Teams with multiple related packages must maintain separate repositories or manually configure workspaces.

Proposed Solution

Add optional monorepo configuration:

Implementation Steps

1. Document workspace structure:

   • packages/ directory for multiple packages
   • Shared pyproject.toml at root for workspace config
   • Per-package pyproject.toml for individual packages

2. Configure uv workspaces in root pyproject.toml:

   • [tool.uv.workspace] section
   • members = ["packages/*"]

3. Update doit tasks to support workspaces:

   • doit test --package=name - Test specific package
   • doit test - Test all packages
   • doit build --package=name - Build specific package

4. Shared configuration:

   • Common ruff/mypy config at root
   • Per-package overrides where needed
   • Shared dev dependencies

5. CI updates: Matrix build for each package or unified build

6. Create example: examples/monorepo/ showing:

   • Core library package
   • CLI package depending on core
   • Shared types package

Documentation

• docs/advanced/monorepo.md explaining setup and tradeoffs

Success Criteria

• Workspace configuration documented
• doit tasks support --package flag
• Example monorepo structure provided
• CI handles multiple packages
• Documentation covers monorepo setup

Additional Context

Complexity: High - Significant changes to build system and CI