Remove linked-issue gate from commitperclip (#7423)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The `commitperclip` PR quality gates enforce hygiene on every PR
before merge
> - One of those gates required PRs to link to a tracking issue, which
adds friction for small/internal changes that don't need a tracker entry
> - The repository owner decided the linked-issue requirement is no
longer the right default
> - This pull request removes the linked-issue gate (the script, its
tests, and the orchestrator wiring)
> - The benefit is fewer false-failing PR checks and one less mandatory
authoring step

## What Changed

- Deleted `.github/scripts/check-pr-linked-issue.mjs`
- Deleted `.github/scripts/tests/check-pr-linked-issue.test.mjs`
- Removed the `checkLinkedIssue` import, the
`Promise.resolve(checkLinkedIssue(...))` entry in the `Promise.all`
block, the `issueResult` destructured binding, and the
`...issueResult.failures` spread from
`.github/scripts/run-quality-gates.mjs`

## Verification

- `node --test .github/scripts/tests/*.test.mjs` — 72/72 tests pass
across the remaining 4 gate suites
- `git grep -n
'check-pr-linked-issue\|checkLinkedIssue\|check-pr-linked'` — no matches
- Inspected `run-quality-gates.mjs` — no orphaned `issueResult`
references

## Risks

- Low risk. Pure removal of one optional gate; the
`.github/workflows/commitperclip-review.yml` workflow only invokes the
orchestrator and needs no changes. PR template and `CONTRIBUTING.md` do
not mention linked issues, so no docs change is required.

## Model Used

- Claude (Anthropic), `claude-opus-4-7`, extended-thinking mode, tool
use enabled

## 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 run tests locally and they pass
- [x] I have added or updated tests where applicable (existing
gate-suite tests still pass; removed gate's tests deleted with it)
- [x] If this change affects the UI, I have included before/after
screenshots (n/a — CI script change)
- [x] I have updated relevant documentation to reflect my changes (no
docs reference the removed gate)
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

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

.github/scripts/check-pr-linked-issue.mjs

@@ -1,53 +0,0 @@
-#!/usr/bin/env node
-/**
- * check-pr-linked-issue.mjs
- * Checks that a PR body references a GitHub issue. Respects conventional commit
- * prefixes — skips check for docs/chore/build/ci/style/test prefixed PRs.
- * Export: checkLinkedIssue(prBody: string, prTitle: string) → { passed, failures }
- */
-import { fileURLToPath } from 'node:url';
-
-const ISSUE_PATTERNS = [
-  /(?:fixes|closes|resolves)\s+#\d+/i,
-  /(?:^|[\s(])https:\/\/github\.com\/paperclipai\/paperclip\/issues\/\d+(?=$|[\s),:;!?]|[.](?![\w-]))/i,
-  /(?<!\w)#\d+/,
-];
-
-// Prefixes where a linked issue is NOT required
-const SKIP_ISSUE_PREFIXES = ['docs', 'chore', 'build', 'ci', 'style', 'test', 'revert'];
-
-function parsePrefix(title) {
-  if (!title) return null;
-  const match = title.match(/^([a-z]+)(?:\([^)]*\))?:/);
-  return match ? match[1].toLowerCase() : null;
-}
-
-export function checkLinkedIssue(body, prTitle = '') {
-  const prefix = parsePrefix(prTitle);
-
-  if (prefix && SKIP_ISSUE_PREFIXES.includes(prefix)) {
-    return { passed: true, failures: [] };
-  }
-
-  if (!body || !body.trim()) {
-    return { passed: false, failures: ['PR body is empty — please fill out the PR template'] };
-  }
-
-  const found = ISSUE_PATTERNS.some(p => p.test(body));
-  return {
-    passed: found,
-    failures: found ? [] : [
-      'No linked issue found — please add `Fixes #NNN` to your PR description. ' +
-      'If no issue exists yet, please file one first: ' +
-      'https://github.com/paperclipai/paperclip/issues/new',
-    ],
-  };
-}
-
-if (process.argv[1] === fileURLToPath(import.meta.url)) {
-  const body = process.env.PR_BODY ?? '';
-  const title = process.env.PR_TITLE ?? '';
-  const result = checkLinkedIssue(body, title);
-  console.log(JSON.stringify(result));
-  process.exit(result.passed ? 0 : 1);
-}