Adopt .chezmoiroot layout to split repo-level and global AGENTS.md

[ahjota]

Problem

This repo's root is the chezmoi source root, so every top-level entry maps 1:1 into ~. That forces AGENTS.md to serve two audiences with one file:

• Repo-level agent instructions (read by Droid/Claude Code/OpenCode sessions working in this repo)
• Global agent guidance (deployed to ~/AGENTS.md, read on every machine)

With the current layout there is no way to give the two audiences different content:

• A second source entry for target ~/AGENTS.md (e.g. symlink_AGENTS.md) is a duplicate-target error.
• .chezmoiignore patterns match target paths, so ignoring AGENTS.md kills every entry targeting ~/AGENTS.md, symlink included.

Related symptom: repo-only files leak into ~ unless explicitly ignored. UNLICENSE-AUDIT.md currently deploys to ~/UNLICENSE-AUDIT.md (only README.md and LICENSE are ignored today).

Goal

• Repo-root AGENTS.md = repo-specific agent instructions only; not deployed.
• home/AGENTS.md = global agent guidance; deployed to ~/AGENTS.md.
• All other deployed targets unchanged.

Approach: .chezmoiroot

Add a repo-root .chezmoiroot file containing home, making home/ the chezmoi source directory. Repo-root files (README.md, LICENSE, AGENTS.md, .github/, etc.) then sit outside the source state entirely and chezmoi never sees them.

Plan

1. Snapshot current state for later diffing:

   chezmoi managed | sort > /tmp/managed-before.txt

2. Create home/ and move the source state into it (use git mv to preserve history):
   • dot_Rprofile.tmpl, dot_bash_profile.tmpl, dot_bashrc.tmpl, dot_claude/, dot_gitconfig.tmpl, dot_gitignore, dot_local/, dot_pip/, dot_profile.tmpl, dot_shellrc.d/, dot_vimrc, dot_zsh_plugins.txt, dot_zshrc.tmpl
   • private_Library/, private_dot_config/, private_dot_factory/, workspace/
   • AGENTS.md → home/AGENTS.md (becomes the global file)
   • .chezmoiignore and .chezmoi.toml.tmpl (special files live in the source root; ignore patterns are target-relative, so their contents don't change)
3. Create repo-root .chezmoiroot containing exactly home.
4. Write the new repo-root AGENTS.md with chezmoi-repo-specific instructions only (Conventional Commits requirement, dot_/.tmpl naming, code review and testing conventions). Keep purely global guidance in home/AGENTS.md.
5. Update .github/prompts/fix-issue.md to note that the chezmoi source state lives under home/.
6. Verify:

   chezmoi source-path          # expect: ~/.local/share/chezmoi/home
   chezmoi managed | sort > /tmp/managed-after.txt
   diff /tmp/managed-before.txt /tmp/managed-after.txt
   chezmoi apply --dry-run --verbose

   Expected diff: ~/UNLICENSE-AUDIT.md is no longer managed (intentional); ~/AGENTS.md remains managed, now sourced from home/AGENTS.md. Nothing else changes.
7. Apply with chezmoi apply, then commit per Conventional Commits.

Acceptance criteria

• chezmoi source-path prints ~/.local/share/chezmoi/home
• chezmoi managed diff vs. pre-migration shows only the UNLICENSE-AUDIT.md removal
• chezmoi apply --dry-run --verbose reports no unexpected changes
• Repo-root AGENTS.md holds repo-specific instructions and is not deployed
• ~/AGENTS.md renders the global guidance from home/AGENTS.md
• droid-issue-fixer workflow and prompt still reference valid paths

Alternatives considered

• One shared file (status quo): works, but repo-specific notes deploy to every machine and the two audiences can't diverge.
• run_after_ script copying a global file to ~/AGENTS.md: works around the 1:1 mapping, but the deployed file becomes invisible to chezmoi status/chezmoi managed, so drift goes undetected.

Notes

• Other machines: chezmoi update picks up .chezmoiroot automatically; deployed targets don't move, so no re-init is needed. Fresh clones: chezmoi init reads .chezmoi.toml.tmpl from the new source root.
• Path references: anything hardcoding ~/.local/share/chezmoi/<file> must now use ~/.local/share/chezmoi/home/<file>.
• History: the move is one large rename commit; git rename detection keeps git log --follow working.

Out of scope

• Changing deployed file contents (other than the AGENTS.md split)
• Reorganizing within home/