docs: discourage utility scripts in package manifests (#16842)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Its review process protects package manifests because they define
dependencies.
> - New convenience scripts also change these protected files and cause
extra review.
> - Greptile needs a clear instruction to discourage these additions.
> - This pull request adds the requested sentence to the Greptile
prompt.

## Linked Issues or Issue Description

**Issue type**

Missing documentation.

**Where is the issue?**

The repository review prompt in `.greptile/rules.md`.

**What's wrong?**

Agents add package scripts for utilities and specialized checks. These
additions trigger the extra review intended for protected package
manifests. No duplicate open PR or issue was found in the GitHub search.

**Suggested fix**

Add this exact instruction: Do not add package.json scripts for new
utilities, checks, benchmarks, or specialized tests.

## What Changed

- Added the requested sentence to `.greptile/rules.md`.

## Verification

- `git diff --check` passed.
- Confirmed that the diff contains only the requested sentence and its
separating blank line.
- Local prompt and PR-template checks passed.
- Full typecheck, test, and build checks were not completed. This
worktree has no installed dependencies. The typecheck attempt stalled
during pnpm startup and was stopped; the test and build commands were
not run.

## Risks

- Low risk. This changes review instructions only. Greptile may flag
future additions in the listed categories.

## Model Used

- OpenAI GPT-6 through Codex, with repository inspection and shell
tools. The exact runtime model ID and context window size were not
exposed to this session. The user supplied the added sentence verbatim.

## 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
- [x] I have run tests locally and they pass (focused prompt and
PR-template checks only; full-suite limits are recorded above)
- [x] I have added or updated tests where applicable (no new tests
needed for this prose-only change)
- [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
- [x] 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>

.greptile/rules.md

@@ -10,3 +10,5 @@ Each rule's YAML frontmatter declares its scope with repository-relative
 do not apply a channel rule to unrelated subsystems. Keep the policy in the
 referenced file as the source of truth rather than maintaining a separate copy
 in dashboard instructions.
+
+Do not add package.json scripts for new utilities, checks, benchmarks, or specialized tests.