refactor(extension): 모듈 분리 + Hub 통합 테스트 #task-395

- extension.ts 3,446→1,289줄 (-63%)
- step-probe.ts (1,435줄): setupMonitor, processResponseFile, tryApprovalStrategies
- observer-script.ts (687줄): DOM observer script
- ws-client.ts (390줄): WSBridgeClient
- step-utils.ts (114줄): step 파싱 유틸
- auth.py (115줄): JWT + registration code
- hub.py (581줄): WSHub + per-client queue
- Hub WS 연동 테스트 통과 (auth, chat, register)
- VSIX v0.4.0 빌드

tests/test_syntax.py

@@ -0,0 +1,28 @@
+"""Quick syntax check for all modified/new Python files."""
+import ast
+import sys
+
+files = [
+    'auth.py',
+    'hub.py', 
+    'config.py',
+    'gateway.py',
+    'main.py',
+    'bot.py',
+]
+
+errors = []
+for f in files:
+    try:
+        with open(f'../{f}', encoding='utf-8') as fh:
+            ast.parse(fh.read())
+        print(f'  OK: {f}')
+    except SyntaxError as e:
+        print(f'  FAIL: {f} - {e}')
+        errors.append(f)
+
+if errors:
+    print(f'\nFailed: {errors}')
+    sys.exit(1)
+else:
+    print('\nAll files parse OK')