fix: guard and document the external tools PR #168 flagged as unguarded

PR #168's Notes section named several functions with a real
external-tool dependency that no `type -q`/`command -q`/`command -v`/
`which` guard covers anywhere in the tree, deliberately left out of
DEPENDENCIES to avoid breaking test_dependencies_resolve. Adds the
guard each was missing, then declares the dependency now that it
resolves:

- bkg, detach: nohup
- gitui: gitui (self-shadow; type -q -f to skip the function itself)
- play-media: mpv, vlc -- already guarded via `type -q -f $p` in a
  loop, just never recognized as one (see next point)
- steam-dl: systemd-inhibit, steam
- wake-lock: systemd-inhibit
- split, spwin, tab: wezterm, konsole (kitty already declared)

docs/verify-manual.py's guard-detection regex only matched `type -q
<name>` immediately, so `type -q -f $p` (the `-f` flag excludes
functions from the match, needed wherever a wrapper shadows a binary
of its own name) was invisible to it -- both as a direct guard and
through the loop-variable indirection. Broadened both patterns to
skip over any flags between `-q` and the name/variable.

split/spwin/tab dispatch on $TERM/$TERM_PROGRAM/$KONSOLE_VERSION to
pick which terminal-specific binary to call, per this repo's C4
convention -- but those env vars only prove the terminal type, not
that its CLI binary is on $PATH: they propagate over ssh, so sshing
out from Kitty/WezTerm inherits the var on a remote host that never
installed the binary. Same latent gap in clone/clonet, whose
clone-in-kitty is a function Kitty's own shell integration injects,
not present on a remote shell that only inherited $TERM. All five now
check the actual thing they are about to call, not just the env var
that selects it.

Also guards and documents three more real, previously-undeclared
dependencies found by the same audit, unrelated to PR #168's named
list but the identical pattern: fast-cli (fast), lock (loginctl),
ports (lsof), screensleep (busctl).

docs/fish-config.md regenerated to match.

functions/spwin.fish

@@ -8,7 +8,7 @@
 #   integrations/window-mgmt
 #
 # DEPENDENCIES
-#   kitty
+#   kitty, wezterm
 #
 # SYNOPSIS
 #   spwin [args...]
@@ -36,13 +36,23 @@ function spwin --wraps='~/.config/kitty/spawn-window.sh' --description 'spawn wi
         return 1
     end
 
+    # $TERM/$TERM_PROGRAM only prove the terminal type, not that its CLI
+    # binary is on $PATH -- e.g. sshing out from Kitty/WezTerm inherits the
+    # env var on the remote host without the binary. Check explicitly.
     if test "$TERM" = xterm-kitty
         if test -x ~/.config/kitty/spawn-window.sh
             ~/.config/kitty/spawn-window.sh $argv
-        else
+        else if type -q kitty
             kitty @ launch --type=window $argv
+        else
+            echo "Error: 'spwin' detected Kitty but neither spawn-window.sh nor the kitty binary is available." >&2
+            return 1
         end
     else if test "$TERM_PROGRAM" = WezTerm
+        if not type -q wezterm
+            echo "Error: 'spwin' detected WezTerm but the wezterm binary is not installed." >&2
+            return 1
+        end
         wezterm cli spawn $argv
     else
         echo "Error: The 'spwin' command requires Kitty or WezTerm." >&2