A home-prefix install puts the plugins outside Qt's default search path, so
Kate would not list them until QT_PLUGIN_PATH includes the install dir — the
step a bare 'cmake --install' silently left undone. Solve it the way the ollie
project does (a Plasma login env snippet), and automate the common case:
- Add 99-deft.sh.in, a Plasma env snippet that prepends the install's qt6
plugin dir to QT_PLUGIN_PATH. configure_file() fills in the absolute path.
- On a user-local install (prefix inside $HOME), install(CODE) drops the
configured 99-deft.sh into ~/.config/plasma-workspace/env/ so the lookup
path is wired up with no manual step; Plasma sources it at next login. The
installer also prints a one-line export to use the plugins immediately.
- On a system-prefix install it does not touch the user's config; it just
prints where the plugins went and leaves the ready snippet in the build dir.
README: add a 'Making Kate find a user-local install' section explaining that
QT_PLUGIN_PATH must include ~/.local, that the installer handles it, and how to
activate it in the current session (or a non-Plasma shell).
Verified: cmake --install with the default prefix installs the six plugins and
writes ~/.config/plasma-workspace/env/99-deft.sh with the correct path.