fix(install): guard Windows desktop installs against broken web_server

scripts/install.ps1

@@ -1995,6 +1995,7 @@ print(','.join(scripts))
     $pythonExe = if (-not $NoVenv) { "$InstallDir\venv\Scripts\python.exe" } else { (& $UvCmd python find $PythonVersion) }
     if (Test-Path $pythonExe) {
         $webOk = $false
+        $webServerSyntaxOk = $false
         # Relax EAP=Stop while running the import probe; see the matching
         # comment on the baseline-imports check above.  Python writes
         # deprecation warnings to stderr and we don't want those wrapped
@@ -2006,6 +2007,10 @@ print(','.join(scripts))
             & $pythonExe -c "import fastapi, uvicorn" 2>&1 | Out-Null
             if ($LASTEXITCODE -eq 0) { $webOk = $true }
         } catch { }
+        try {
+            & $pythonExe -m py_compile "$InstallDir\hermes_cli\web_server.py" 2>&1 | Out-Null
+            if ($LASTEXITCODE -eq 0) { $webServerSyntaxOk = $true }
+        } catch { }
         $ErrorActionPreference = $prevEAP
         if (-not $webOk) {
             Write-Warn "fastapi/uvicorn not importable -- `hermes dashboard` will not work."
@@ -2017,6 +2022,9 @@ print(','.join(scripts))
                 Write-Warn "Could not install [web] extra. Run manually: uv pip install --python `"$pythonExe`" `"fastapi>=0.104,<1`" `"uvicorn[standard]>=0.24,<1`""
             }
         }
+        if (-not $webServerSyntaxOk) {
+            throw "dashboard backend source failed syntax check: hermes_cli/web_server.py"
+        }
     }
     
     Pop-Location