feat: listener retry override, pool protocol filter, conn pool docs

- Per-listener `retries` overrides global default (0 = inherit)
- Pool-level `allowed_protos` filters proxies during merge
- Connection pooling documented in CHEATSHEET.md
- Both features exposed in /config and /status API responses
- 12 new tests (config parsing, API exposure, merge filtering)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_pool.py

@@ -171,6 +171,46 @@ class TestProxyPoolMerge:
         assert pool.count == 1
 
 
+class TestProxyPoolAllowedProtos:
+    """Test pool-level proxy protocol filter."""
+
+    def test_allowed_protos_filters_merge(self):
+        cfg = ProxyPoolConfig(sources=[], allowed_protos=["socks5"])
+        pool = ProxyPool(cfg, [], timeout=10.0)
+        proxies = [
+            ChainHop(proto="socks5", host="1.2.3.4", port=1080),
+            ChainHop(proto="http", host="5.6.7.8", port=8080),
+            ChainHop(proto="socks4", host="9.9.9.9", port=1080),
+        ]
+        pool._merge(proxies)
+        assert pool.count == 1
+        assert "socks5://1.2.3.4:1080" in pool._proxies
+
+    def test_allowed_protos_multiple(self):
+        cfg = ProxyPoolConfig(sources=[], allowed_protos=["socks5", "http"])
+        pool = ProxyPool(cfg, [], timeout=10.0)
+        proxies = [
+            ChainHop(proto="socks5", host="1.2.3.4", port=1080),
+            ChainHop(proto="http", host="5.6.7.8", port=8080),
+            ChainHop(proto="socks4", host="9.9.9.9", port=1080),
+        ]
+        pool._merge(proxies)
+        assert pool.count == 2
+        assert "socks5://1.2.3.4:1080" in pool._proxies
+        assert "http://5.6.7.8:8080" in pool._proxies
+        assert "socks4://9.9.9.9:1080" not in pool._proxies
+
+    def test_empty_allowed_protos_accepts_all(self):
+        cfg = ProxyPoolConfig(sources=[], allowed_protos=[])
+        pool = ProxyPool(cfg, [], timeout=10.0)
+        proxies = [
+            ChainHop(proto="socks5", host="1.2.3.4", port=1080),
+            ChainHop(proto="http", host="5.6.7.8", port=8080),
+        ]
+        pool._merge(proxies)
+        assert pool.count == 2
+
+
 class TestProxyPoolGet:
     """Test proxy selection."""