Default local build working directory to repo-local build/ and install/ (#4)

Change TempDir default from $env:TEMP to build/ in the repo root, and
InstallDir from C:\quantlib-build\install to install/ in the repo root.
This lets you inspect patched QuantLib sources after a local build.
CI is unaffected since the workflow passes explicit paths.

https://claude.ai/code/session_01EVB6yo51Ug6uCWAPSfUgwz

Co-authored-by: Claude <noreply@anthropic.com>

Author: fumitoh

README.md

@@ -34,6 +34,8 @@ Requirements: Visual Studio 2022 (C++ workload), CMake, 7-Zip.
 .\scripts\Build-QuantLibDLL.ps1 -PackageZip
 ```
 
+By default the working directory is `build/` and the install directory is `install/` inside the repo, so you can inspect the patched QuantLib sources at `build\QuantLib-<version>\` after the build.
+
 With custom versions and install location:
 
 ```powershell

scripts/Build-QuantLibDLL.ps1

@@ -23,9 +23,11 @@
 
 .PARAMETER InstallDir
     Where to install QuantLib (cmake --install prefix).
+    Default: install/ in the repository root.
 
 .PARAMETER TempDir
-    Temporary directory for source downloads and build artifacts.
+    Working directory for source downloads and build artifacts.
+    Default: build/ in the repository root so you can inspect patched sources.
 
 .PARAMETER Jobs
     Number of parallel build jobs. 0 = auto-detect (default).
@@ -50,8 +52,8 @@
 param(
     [string]$QuantLibVersion = "1.41",
     [string]$BoostVersion    = "1.87.0",
-    [string]$InstallDir      = "C:\quantlib-build\install",
-    [string]$TempDir         = "$env:TEMP\quantlib-dll-build",
+    [string]$InstallDir      = (Join-Path (Split-Path $PSScriptRoot) "install"),
+    [string]$TempDir         = (Join-Path (Split-Path $PSScriptRoot) "build"),
     [int]$Jobs               = 0,
     [switch]$BuildTests,
     [switch]$PackageZip,