Add an Uninstall button on installed external plugin cards that deletes
the package folder (effective next restart — the library stays resident
for the session). Reinstalling or upgrading via the marketplace now
clears any stale native library with a different name before writing the
new one, so the loader always picks the freshly installed binary.
Part of the #100 extensibility epic (phase 2).
Co-Authored-By: Claude Opus 4.8 <[email protected]>