feat(collection): PostgreSQL 백킹 활성화 (CollectionRepository + TokenCache)

- Program.cs: PlaceholderCollectionRepository/TokenCache/KisApiClient → 실제 구현체로 변경
- 데이터베이스 초기화: EnsureTablesAsync() 호출 (시작 시 테이블 자동 생성)
- kis_tokens, kis_collection_runs, kis_collection_snapshots, kis_collection_errors 테이블
- Dapper 기반 SQL 쿼리 (파라미터화, SQL 주입 방지)
- 인덱스: started_at, ticker, captured_at, run_id
- PlaceholderImplementations.cs 제거

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/dotnet/QuantEngine.Core/bin/Debug/net10.0/QuantEngine.Core.deps.json

@@ -0,0 +1,23 @@
+{
+  "runtimeTarget": {
+    "name": ".NETCoreApp,Version=v10.0",
+    "signature": ""
+  },
+  "compilationOptions": {},
+  "targets": {
+    ".NETCoreApp,Version=v10.0": {
+      "QuantEngine.Core/1.0.0": {
+        "runtime": {
+          "QuantEngine.Core.dll": {}
+        }
+      }
+    }
+  },
+  "libraries": {
+    "QuantEngine.Core/1.0.0": {
+      "type": "project",
+      "serviceable": false,
+      "sha512": ""
+    }
+  }
+}

src/dotnet/QuantEngine.Core/obj/Debug/net10.0/.NETCoreApp,Version=v10.0.AssemblyAttributes.cs

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+// <autogenerated />
+using System;
+using System.Reflection;
+[assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v10.0", FrameworkDisplayName = ".NET 10.0")]

src/dotnet/QuantEngine.Core/obj/Debug/net10.0/QuantEngine.Core.AssemblyInfo.cs

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+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+using System;
+using System.Reflection;
+
+[assembly: System.Reflection.AssemblyCompanyAttribute("QuantEngine.Core")]
+[assembly: System.Reflection.AssemblyConfigurationAttribute("Debug")]
+[assembly: System.Reflection.AssemblyFileVersionAttribute("1.0.0.0")]
+[assembly: System.Reflection.AssemblyInformationalVersionAttribute("1.0.0+4ef7a54ad55182e164ca78e8af21f2a5e214c98f")]
+[assembly: System.Reflection.AssemblyProductAttribute("QuantEngine.Core")]
+[assembly: System.Reflection.AssemblyTitleAttribute("QuantEngine.Core")]
+[assembly: System.Reflection.AssemblyVersionAttribute("1.0.0.0")]
+
+// Generated by the MSBuild WriteCodeFragment class.
+

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+C:\Temp\data_feed\src\dotnet\QuantEngine.Core\bin\Debug\net10.0\QuantEngine.Core.dll
+C:\Temp\data_feed\src\dotnet\QuantEngine.Core\bin\Debug\net10.0\QuantEngine.Core.pdb
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+C:\Temp\data_feed\src\dotnet\QuantEngine.Core\obj\Debug\net10.0\QuantEngine.Core.dll
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