Automate manpage generation from argparse definitions

[Copilot]

Manpage generation was previously manual and prone to drift from actual CLI behavior. This PR automates generation from argparse definitions using argparse-manpage.

Changes

• Makefile automation: Added targets for wheel, manpages, test, and clean. The wheel target depends on manpages to ensure manpage is regenerated on builds.

• argparse integration: Extracted get_parser() function in __main__.py for argparse-manpage compatibility. The manpage is now generated from the actual argument parser definitions.

• Documentation structure: Added man/extra-sections.man containing EXPRESSIONS, EXAMPLES, and other sections not derivable from argparse. The generated man/datetimecalc.1 combines argparse-derived content with these manual sections.

• Build artifact handling: Added man/*.1 to .gitignore since manpages are now generated at build time, not committed to version control.

• CI integration: Updated wheel.yml workflow to use make wheel instead of direct uv build calls.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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