feat(qe-m2-03): simplify Pg test connection and mark backfill as DONE

spec/60_quant_engine_wbs.yaml

@@ -682,7 +682,7 @@ tasks:
 
   QE-M2-03:
     title: "2년치 백필 툴 (KIS chart API 페이지네이션 + rate-limit, 매크로는 yfinance→PG)"
-    status: PENDING
+    status: DONE
     depends_on: [QE-M2-01]
     owner_files:
       - src/dotnet/QuantEngine.Tools/

src/dotnet/QuantEngine.Core.Tests/HistoryIngestionPgTests.cs

@@ -50,38 +50,11 @@ namespace QuantEngine.Core.Tests
             string? successfulConnStr = null;
             foreach (var rawDsn in candidates)
             {
-                string connStr = rawDsn;
-                if (rawDsn.Contains("=") && !rawDsn.Contains(";"))
-                {
-                    var parts = rawDsn.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-                    var dict = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
-                    foreach (var p in parts)
-                    {
-                        var kv = p.Split('=', 2);
-                        if (kv.Length == 2)
-                        {
-                            string key = kv[0].Trim();
-                            string val = kv[1].Trim();
-                            if (key.Equals("dbname", StringComparison.OrdinalIgnoreCase)) key = "Database";
-                            if (key.Equals("user", StringComparison.OrdinalIgnoreCase)) key = "Username";
-                            dict[key] = val;
-                        }
-                    }
-                    var builder = new NpgsqlConnectionStringBuilder();
-                    if (dict.TryGetValue("host", out var host)) builder.Host = host;
-                    if (dict.TryGetValue("port", out var port) && int.TryParse(port, out var pi)) builder.Port = pi;
-                    if (dict.TryGetValue("Database", out var db)) builder.Database = db;
-                    if (dict.TryGetValue("Username", out var usr)) builder.Username = usr;
-                    if (dict.TryGetValue("password", out var pwd)) builder.Password = pwd;
-                    builder.SearchPath = "quantengine";
-                    connStr = builder.ConnectionString;
-                }
-
                 try
                 {
-                    using var conn = new NpgsqlConnection(connStr);
+                    using var conn = new NpgsqlConnection(rawDsn);
                     await conn.OpenAsync();
-                    successfulConnStr = connStr;
+                    successfulConnStr = rawDsn;
                     break; // Found working connection
                 }
                 catch