chore: ignore personal agent instructions (#16970)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Contributors use repository instructions to guide their local
agents.
> - Personal instructions can differ between contributors.
> - A root `AGENTS.local.md` file can hold these personal additions.
> - Git must keep this file out of shared commits by default.
> - This pull request adds a root ignore rule for the file.

## Linked Issues or Issue Description

**What existing behavior does this improve?**

Git ignore rules for personal agent instructions in a local checkout.

**Current behavior**

Git lists a root `AGENTS.local.md` as an untracked file. A contributor
can add it to a commit by mistake.

**Proposed behavior**

Git ignores the root `AGENTS.local.md` by default. Each contributor can
keep personal instructions in that file.

**Reason and benefit**

Personal agent settings stay local. Contributors can keep using the
shared `AGENTS.md` for repository rules.

**Breaking changes**

None. The rule applies only to an untracked file at the repository root.

No related public issues or pull requests appeared in searches for
`AGENTS.local.md`.

## What Changed

- Add `/AGENTS.local.md` to `.gitignore` under a personal agent
instructions comment.

## Verification

- `git check-ignore -v AGENTS.local.md` selects the new root ignore
rule.
- `git ls-files AGENTS.local.md` returns no tracked files.
- `git diff --name-only origin/master...HEAD` lists only `.gitignore`.
- `git diff --check origin/master...HEAD` passes.
- `pnpm -r typecheck`, `pnpm test:run`, and `pnpm build` were attempted.
All three stopped before execution because pnpm could not fetch and
verify the pinned `pnpm@9.15.4` through the network sandbox. This
checkout also has no installed dependencies. The Git checks above
passed. CI status remains separate.

## Risks

Low risk. Git will hide a root `AGENTS.local.md` from normal staging.
Existing tracked files remain tracked. The ignore rule does not make
Codex load the file; contributors must configure that separately.

## Model Used

OpenAI Codex (GPT-6), with file editing, shell execution, and GitHub
tools. The exact backend model ID and context window were not exposed in
this session.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [ ] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [ ] All Paperclip CI gates are green
- [ ] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Paperclip <noreply@paperclip.ing>

.gitignore

@@ -60,6 +60,9 @@ diagnostics/
 /.idea/
 /.agents/
 
+# Personal agent instructions
+/AGENTS.local.md
+
 # Doc maintenance cursor
 .doc-review-cursor