refactor: rename stock-lab → stock (graduation)

- git mv stock-lab/ → stock/
- docker-compose.yml: 서비스 키 + container_name + build.context +
  frontend.depends_on + agent-office STOCK_LAB_URL → STOCK_URL
- agent-office/app: config.py, service_proxy.py, agents/stock.py, tests/
  STOCK_LAB_URL → STOCK_URL
- nginx/default.conf: proxy_pass http://stock-lab → http://stock (3 lines)
- CLAUDE.md / README.md / STATUS.md / scripts/ 문구 갱신
- stock/ 내부 자기 참조 갱신

lab 네이밍 정책 (feedback_lab_naming.md) graduation.
API URL / Python import / DB 파일명 변경 없음.

stock/app/screener/nodes/base.py

@@ -0,0 +1,40 @@
+"""Node base classes + helpers."""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Any, ClassVar
+
+import pandas as pd
+
+
+class ScoreNode(ABC):
+    name:           ClassVar[str]
+    label:          ClassVar[str]
+    default_params: ClassVar[dict]
+    param_schema:   ClassVar[dict]
+
+    @abstractmethod
+    def compute(self, ctx: "Any", params: dict) -> pd.Series:
+        """returns Series indexed by ticker, 0..100 float."""
+
+
+class GateNode(ABC):
+    name:           ClassVar[str]
+    label:          ClassVar[str]
+    default_params: ClassVar[dict]
+    param_schema:   ClassVar[dict]
+
+    @abstractmethod
+    def filter(self, ctx: "Any", params: dict) -> pd.Index:
+        """returns surviving tickers."""
+
+
+def percentile_rank(series: pd.Series) -> pd.Series:
+    """Percentile rank in [0, 100]. All-equal → 50. NaN preserved."""
+    if series.empty:
+        return series.astype(float)
+    if series.dropna().nunique() == 1:
+        return pd.Series(50.0, index=series.index)
+    ranked = series.rank(pct=True, na_option="keep") * 100.0
+    return ranked