ci(lint): drop actions/setup-python; use host Python in machine PATH

The runner's act_runner runs as SYSTEM, which only sees the Machine PATH.
Host has Python 3.14 installed at C:\Program Files\Python314\; once that
path is added to the machine PATH (one-time admin op) the simple
Get-Command python lookup works without network downloads.

.gitea/workflows/lint.yml

@@ -80,9 +80,12 @@ jobs:
         run: |
           $ErrorActionPreference = 'Stop'
 
-          # python is provided by actions/setup-python and is on PATH for this step.
+          # python is provided by the host (machine-wide install in PATH).
+          # Requires Python >=3.11 per pyproject.toml.
           $py = (Get-Command python -ErrorAction Stop).Source
           Write-Host "Using python: $py"
+          & $py --version
+          if ($LASTEXITCODE -ne 0) { throw "python --version failed" }
 
           if (-not (Test-Path "$env:VENV_DIR\Scripts\python.exe")) {
             Write-Host "Creating venv at $env:VENV_DIR"