config(fish): add fish completions for cli tools

dot_config/fish/functions/clear.fish

@@ -0,0 +1,11 @@
+function clear --wraps clear --description 'clear screen + kitty scrollback, prompt pinned to the bottom'
+    if not status is-interactive
+        command clear $argv
+        return
+    end
+    # kitty doesn't clear scrollback with plain `clear`; 3J drops it.
+    printf '\033[2J\033[3J\033[1;1H'
+    # Re-pin only when the bottom prompt is enabled (FISH_BOTTOM_PROMPT=0
+    # keeps the default top prompt).
+    test "$FISH_BOTTOM_PROMPT" = 1; and tput cup $LINES 0
+end