CI(windows): per-user Python install + robust python.exe path lookup

The installer's InstallAllUsers=1 needs admin (runner service isn't elevated)
so Python landed in the per-user LOCALAPPDATA dir, not C:\Program Files; the
hardcoded PATH prepend missed it -> 'python not recognized'. Switch to a
per-user install and locate python.exe across the known dirs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016yT89n4zR4qbrySoSiEyZs

.gitea/workflows/release.yml

@@ -18,11 +18,17 @@ jobs:
         run: |
           $ErrorActionPreference = "Stop"
           if (-not (Get-Command python -ErrorAction SilentlyContinue)) {
-            Write-Host "Python not found; installing 3.12..."
+            Write-Host "Python not found; installing 3.12 (per-user, no admin needed)..."
             $url = "https://www.python.org/ftp/python/3.12.7/python-3.12.7-amd64.exe"
             Invoke-WebRequest -Uri $url -OutFile "$env:TEMP\py.exe"
-            Start-Process -Wait -FilePath "$env:TEMP\py.exe" -ArgumentList "/quiet","InstallAllUsers=1","PrependPath=1","Include_test=0"
-            $env:Path = "C:\Program Files\Python312;C:\Program Files\Python312\Scripts;$env:Path"
+            Start-Process -Wait -FilePath "$env:TEMP\py.exe" -ArgumentList "/quiet","PrependPath=1","Include_test=0"
+            $base = @(
+              "$env:LOCALAPPDATA\Programs\Python\Python312",
+              "C:\Program Files\Python312",
+              "C:\Python312"
+            ) | Where-Object { Test-Path "$_\python.exe" } | Select-Object -First 1
+            if (-not $base) { throw "Python install did not produce python.exe in a known location" }
+            $env:Path = "$base;$base\Scripts;$env:Path"
           }
           python --version
           python -m pip install --upgrade pip