refactor(server): migrate to pool-based crawler management

Replace crawler_manager.py with simpler crawler_pool.py implementation:
- Add global page semaphore for hard concurrency cap
- Implement browser pool with idle cleanup
- Add playground UI for testing and stress testing
- Update API handlers to use pooled crawlers
- Enhance logging levels and symbols

BREAKING CHANGE: Removes CrawlerManager class in favor of simpler pool-based approach

tests/memory/test_docker_congif_gen.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""
+Quick sanity‑check for /config/dump endpoint.
+
+Usage:
+    python test_config_dump.py  [http://localhost:8020]
+
+If the server isn’t running, start it first:
+    uvicorn deploy.docker.server:app --port 8020
+"""
+
+import sys, json, textwrap, requests
+
+BASE = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8020"
+URL  = f"{BASE.rstrip('/')}/config/dump"
+
+CASES = [
+    # --- CrawlRunConfig variants ---
+    "CrawlerRunConfig()",
+    "CrawlerRunConfig(stream=True, cache_mode=CacheMode.BYPASS)",
+    "CrawlerRunConfig(js_only=True, wait_until='networkidle')",
+
+    # --- BrowserConfig variants ---
+    "BrowserConfig()",
+    "BrowserConfig(headless=False, extra_args=['--disable-gpu'])",
+    "BrowserConfig(browser_mode='builtin', proxy='http://1.2.3.4:8080')",
+]
+
+for code in CASES:
+    print("\n===  POST:", code)
+    resp = requests.post(URL, json={"code": code}, timeout=15)
+    if resp.ok:
+        print(json.dumps(resp.json(), indent=2)[:400] + "...")
+    else:
+        print("ERROR", resp.status_code, resp.text[:200])