Revert "Remove linked-issue gate from commitperclip" (#7426)

Reverts paperclipai/paperclip#7423

Decided to keep this in place so we can automate issue reproduction in
the future. We all make mistakes. Even me, if you can believe it.

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

@@ -0,0 +1,53 @@
+#!/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);
+}