Add session-handoff skill

[spences10]

Summary

Add a /handoff skill that generates a handoff document for session continuity.

What it does

Generate a concise handoff doc containing:

• What was worked on (from git diff/log)
• Current state (passing tests? lint clean? build working?)
• What's in progress / unfinished
• Decisions made and why
• Known blockers or open questions
• Suggested next steps

Output to .claude/handoff.md (or similar) so next session can /read it to pick up context.

Why

Context resets between sessions. Starting cold means re-discovering state, re-reading files, re-understanding decisions. A handoff doc bridges that gap.

Prior art

• pro-workflow's session-handoff skill: https://github.com/rohitg00/pro-workflow/tree/main/skills/session-handoff

Notes

• Should be lightweight — one page max
• Pair naturally with /wrap-up (wrap-up captures learnings, handoff captures state)
• Could overwrite previous handoff each time (it's ephemeral by nature)