Create standup-prep skill

[timirwin]

Why

Often it is difficult to remember all of the context for a standup update so assist people in pulling it all together. This skill interviews the person against what git, GitHub, Linear, Harvest, Almanac, and Slack actually show, so they arrive with a specific, verified update instead.

What Changed

• Add standup-prep skill: interviews the user one question at a time and produces read-aloud prose for the four standup questions
• Scope every source (Linear, GitHub, Harvest, Almanac, Slack) to the chosen project, with leads getting a second, separate cross-project pass
• Pull Harvest timer comments as a source for work that never touches git or Linear
• Register the skill in README.md and AGENTS.md

Screenshots

N/A — no UI changes

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Pre-merge

• Have you updated README.md and AGENTS.md? Any new, renamed, or removed skill needs a row in the README table and a bullet in AGENTS.md. Check the box or replace it with N/A if this PR touches no skill.