config(fish): add fish completions for cli tools

dot_config/fish/functions/launch_omp_livediff_overlay.fish

@@ -0,0 +1,16 @@
+function launch_omp_livediff_overlay --description "Overlay omp on the current kitty window with a livediff split beside it"
+    # kitty appends -PID to config-file listen_on sockets, so a hardcoded
+    # --to unix:@kitty-local never matches. kitty @ resolves the real
+    # address from $KITTY_LISTEN_ON on its own.
+    if not set -q KITTY_LISTEN_ON
+        echo "launch_omp_livediff_overlay: no kitty remote-control socket (KITTY_LISTEN_ON unset)" >&2
+        return 1
+    end
+
+    # omp overlays the current window; capture its window id
+    set -l wid (kitty @ launch --type=overlay-main --cwd=current omp)
+    or return
+
+    # livediff side by side in the same tab; keep focus on omp
+    kitty @ launch --match id:$wid --location=vsplit --keep-focus --cwd=current livediff
+end