fix: a link opens lazysecrets with your cache and next to your running instances

The link handler's window starts with an app's minimal environment, and only PATH, the config locations and XDG_CONFIG_HOME/XDG_STATE_HOME were carried into it. With XDG_CACHE_HOME or XDG_RUNTIME_DIR set, lazysecrets opened from a link used another cache file and didn't see running instances' sockets; on Linux, without XDG_DATA_HOME it looked for its desktop entry in the wrong place. `handler install` now records those three too: run it again to pick them up.

docs/sharing.md

@@ -143,9 +143,10 @@ turns the question off too.
 link then opens a new window of the terminal you ran it in, with
 lazysecrets on that link. It recognises kitty, Ghostty, WezTerm, iTerm2,
 Terminal.app, Alacritty, GNOME Terminal, Konsole and foot, also inside
-tmux; `--terminal NAME` picks another. It records your `PATH` and config
-locations, since apps start without your shell's environment (and so
-without `az`): run it again after moving lazysecrets or changing those.
+tmux; `--terminal NAME` picks another. It records your `PATH`, config
+locations and XDG directories, since apps start without your shell's
+environment (and so without `az`): run it again after moving lazysecrets
+or changing those.
 
 - macOS: a small background app, `~/Applications/Lazysecrets Links.app`
 - Linux: a desktop entry claiming `x-scheme-handler/lazysecrets`, set as