install.sh doesn't scaffold working artifact directories

[jerseycheese]

Summary

install.sh creates .agents/skills/, .agents/style/, and .agents/prompts/custom/ but does not create the working artifact directories that skills write to: .agents/handoffs/, .agents/plans/, .agents/reviews/, and .agents/lessons/.

Skills that write to these paths (handoff-message, issue-plan, lessons-learned, browser-check) will either fail or create directories in unexpected locations on a fresh install. The README acknowledges these artifacts exist but leaves their location unspecified, which leads users to store them in ad-hoc external locations rather than the natural .agents/ home.

Expected behavior

install.sh scaffolds all directories that skills write to:

.agents/
├── handoffs/      # handoff-message writes here
├── plans/         # issue-plan writes here
├── reviews/       # browser-check saves screenshots here
└── lessons/       # lessons-learned writes here

These are personal working artifacts and should not be tracked in version control. Each directory is created empty, and .git/info/exclude (not .gitignore) is updated to cover their contents so nothing bleeds into git.

Actual behavior

Directories are not created. First skill invocations that write files fail or create directories in unexpected locations.

Additional context

The README notes: "Working artifacts (plans, handoffs, reviews, drafts) are personal/local and git-ignored" — but install.sh never creates those directories or sets up the exclude entries. The gap encourages ad-hoc workarounds.