Add a 'standup' one-shot mode #6

What

A commit-chronicle standup subcommand (or --standup flag) that runs the most common daily use case in one shot, no interactive picker:

• window = last workday (yesterday, but skip back over weekends — e.g. Monday reports Friday)
• behaves like --all --no-edit --copy
• prints the worklog and copies it to the clipboard

Why

This is the single most frequent real use (prepping a daily standup) and currently requires walking the full range → pick → edit → export flow every morning.

Notes

• "Last workday" logic should live alongside the presets in internal/model/range.go.
• Honor existing repo/author config so it works with zero extra flags.
• Could compose with the summary line (Rewrite commit-chronicle as a self-contained Go binary #1) and AI summary features once available.

Relates to the feature brainstorm in chat (#3).