fix: 3 syntax errors in perf_bottleneck_finder.py (#211)

1. Line 116: regex pattern had broken quote escaping
2. Lines 509-510: return statement split across two lines
3. Line 524: global declaration after first use

scripts/perf_bottleneck_finder.py

@@ -113,7 +113,7 @@ def find_slow_tests_by_scan(repo_path: str) -> List[Bottleneck]:
         (r"time\.sleep\((\d+(?:\.\d+)?)\)", "Contains time.sleep() — consider using mock or async wait"),
         (r"subprocess\.run\(.*timeout=(\d+)", "Subprocess with timeout — may block test"),
         (r"requests\.(get|post|put|delete)\(", "Real HTTP call — mock with responses or httpretty"),
-        (r"open\([^)]*['"]w['"]", "File I/O in test — use tmp_path fixture"),
+        (r'open\([^)]*[\x27\x22]w[\x27\x22]', "File I/O in test — use tmp_path fixture"),
     ]
 
     for root, dirs, files in os.walk(repo_path):
@@ -506,8 +506,8 @@ def format_markdown(report: PerfReport) -> str:
                 lines.append(f"- {icon} {b.name}{loc} — ~{b.duration_s:.1f}s — {b.recommendation}")
             lines.append(f"")
 
-    return "
-".join(lines)
+    return "\n".join(lines)
+
 
 
 # ── Main ───────────────────────────────────────────────────────────
@@ -521,7 +521,7 @@ def main():
                         help="Slow test threshold in seconds")
     args = parser.parse_args()
 
-    global SLOW_TEST_THRESHOLD_S
+    # SLOW_TEST_THRESHOLD_S is module-level
     SLOW_TEST_THRESHOLD_S = args.threshold
 
     if not os.path.isdir(args.repo):