fix(build): select the core Zig project explicitly

• ed95d55cab fix(build): select the core Zig project explicitly Chris Breuer review this step
• 171dd39eb5 test(build): exercise core selection with the pinned Windows compiler Chris Breuer review this step
• 05facfdeac test(build): record native checkout project availability Chris Breuer review this step
• 053882af45 test(build): reproduce the native checkout volume Chris Breuer review this step
• eaddd669dd test(build): qualify the Windows build before the regression fixture Chris Breuer review this step