fix: remove invalid backtick before colon in PowerShell string

Line 205 had '$dir`: $_' which is invalid PowerShell syntax.
Changed to '$dir': $_' (regular colon without backtick escape).

PowerShell backticks are only needed for:
- Escape sequences (`n for newline, `t for tab)
- Line continuation
- Escaping special chars like $, `, "

Colons in strings don't need escaping and the backtick was causing
'missing terminator' parse errors.

scripts/verify-build-environment.ps1

@@ -202,7 +202,7 @@ function Clean-CMakeCache {
                 $cleaned = $true
                 Write-Status "  ✓ Removed '$dir'" "Success"
             } catch {
-                Write-Status "  ✗ Failed to remove '$dir`: $_" "Error"
+                Write-Status "  ✗ Failed to remove '$dir': $_" "Error"
                 $script:warnings += "Could not fully clean '$dir' (some files may be locked)"
             }
         }