1.3.5 — Steady Mercury (hotfix: Windows installer on PowerShell 5.1; Linux baseline fallback)

• irm mercuryagent.sh/install.ps1 | iex failed with "checksums.txt must contain exactly one checksum for mercury-win-x64.exe" on stock Windows PowerShell 5.1 — and the window closed before you could read it. GitHub serves checksums.txt as application/octet-stream, for which PowerShell 5.1 returns a byte[] from Invoke-WebRequest; the installer now decodes it (PowerShell 7 was unaffected). A failure now waits for Enter before closing the window (MERCURY_NO_PAUSE=1 for automation).
• Running the saved script (powershell -File install.ps1) failed to parse under PowerShell 5.1: the file had UTF-8 characters and no BOM, so the ANSI code page turned a ✓ into a quote. The installers are ASCII-only now.
• CI runs the Windows installer under PowerShell 5.1 against a local release served as application/octet-stream.
• install.sh (1.3.4) died with "Illegal instruction" instead of switching to the baseline build when the default build crashed in the smoke test (set -e on a failing command substitution). Fixed; the CPU-detection path that picks baseline up front was unaffected.