fix(#211): Fix two SyntaxErrors in perf_bottleneck_finder.py

- Line 116: Fixed quote escaping in open() regex pattern
- Lines 509-510: Fixed split string literal in return statement
- Verified: python3 -m py_compile succeeds

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\\([^)]*['\"]w['\"]", "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)
+
 
 
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