Fix Windows installer to perform in-place upgrades

[elcruzo]

Summary

• Root cause: NSIS script embedded TRACE_VERSION in install path (Trace\1.2.0), registry keys (Trace 1.2.0), shortcuts, file associations, and mutex — causing each version to install as a completely separate application instead of upgrading in-place
• Removed version from all install identifiers (install dir, registry keys, Start Menu path, shortcuts, file associations, AppModelId, mutex) so new versions overwrite the previous installation at C:\Program Files\Trace\
• Added RemoveOldVersionedInstalls migration function that runs on install to detect and silently remove old versioned installations (1.0.0, 1.1.0, 1.2.0) via registry lookup + silent uninstall + stale directory/shortcut cleanup
• Display name in Add/Remove Programs still shows version (e.g. "Trace 1.3.0") so users know which version they have

Test plan

• Build the installer with a test version (e.g. 1.3.0)
• Install on a machine that has an existing versioned install (e.g. 1.1.0 or 1.2.0 at C:\Program Files\Trace\1.2.0\)
• Verify the old versioned install is silently removed during installation
• Verify new install goes to C:\Program Files\Trace\ (no version subfolder)
• Verify only one "Trace" entry appears in Add/Remove Programs (not "Trace 1.1.0" + "Trace 1.3.0")
• Verify Start Menu shortcut is Trace not Trace 1.3.0
• Verify Desktop shortcut is Trace not Trace 1.3.0
• Verify uninstaller correctly removes the non-versioned install
• Test fresh install on a clean machine (no previous versions)