feat(M02): 조합 키 하나 읽기 /api/m02/combos/key/{키} — 어느 층이든 · 그 층 읽기 권한(PLAN 27-2c 서버)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BU9gbNE3aWFUvE61pS2WGt

M02_MasterTemplete/M02_MasterTemplete_Router_Combos.py

@@ -67,6 +67,16 @@ def get_all(session: Session = Depends(verify_session)) -> list[dict]:
     return out
 
 
+@router.get("/combos/key/{key}")
+def get_by_key(key: str, session: Session = Depends(verify_session)) -> dict:
+    """키 하나(어느 층이든 · 그 층 읽기 권한) — `{layer, owner, 판, combo, 줄, …}`."""
+    got = combos.where(key)
+    if got is None:
+        raise HTTPException(status_code=404, detail=f"없는 조합 「{key}」")
+    layer, owner = got
+    return {"layer": layer, "owner": owner, **_call(_root(session, layer, owner), combos.one, key)}
+
+
 @router.get("/layers/{layer}/combos")
 def get_combos(layer: Layer, owner: str | None = None, session: Session = Depends(verify_session)):
     return _call(_root(session, layer, owner), combos.listing)