feat: generate and package man pages via clap-mangen

[aishagbadamosi]

Add build-time man page generation using clap-mangen (v0.2.21) and a runtime starforge man subcommand for viewing/installing them.

Changes:

• build.rs generates 75 man pages (starforge.1 + all subcommands) to man/
• starforge man generate <page> prints roff to stdout for piping into man(1)
• starforge man install --directory <dir> copies pages to a target path
• starforge man list shows all available pages
• Release tarballs (Linux/macOS) now include man/ directory
• install.sh and Homebrew formula install man pages to system paths
• 9 integration tests covering primary flow, boundary, and failure cases

closes #675

Description

Add build-time man page generation using clap-mangen (v0.2.21) and a runtime
starforge man subcommand for viewing/installing them.

Changes:

• build.rs generates 75 man pages (starforge.1 + all subcommands) to man/
• starforge man generate <page> prints roff to stdout for piping into man(1)
• starforge man install --directory <dir> copies pages to a target path
• starforge man list shows all available pages
• Release tarballs (Linux/macOS) now include man/ directory
• install.sh and Homebrew formula install man pages to system paths
• 9 integration tests covering primary flow, boundary, and failure cases
  Closes [2026 Documentation] Generate and package man pages #675

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Changes Made

• Change 1
• Change 2
• Change 3

Testing

How has this been tested?

Describe the tests you ran and how to reproduce them.

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Coverage

Describe what scenarios have been tested:

• Happy path:
• Edge cases:
• Error handling:

Code Quality Checklist

• My code follows the style guidelines of this project (cargo fmt)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings (cargo clippy -- -D warnings)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The CI checks pass (format, clippy, tests)

Breaking Changes

• This PR introduces breaking changes

If checked, describe the breaking changes and migration path:

Documentation

• README.md updated
• DEVELOPER_GUIDE.md updated (if applicable)
• API_REFERENCE.md updated (if applicable)
• No documentation changes needed

Screenshots (if applicable)

Add screenshots or GIFs for UI changes.

Additional Context

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Note: Make sure all tests pass locally before submitting:

cargo test
cargo fmt --all
cargo clippy -- -D warnings

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