feat(help): header-driven --help for terminal and session functions

spwin, tab, hist, bkg, wake-lock and fc take the standard first-arg-only
call site, so `wake-lock rsync --help` still runs rsync.

split takes --help only: its own ARGUMENTS documents -h as --horizontal,
so a literal test replaces the renderer's own flag check. Verified that
`split -h` still selects a horizontal split and never prints help.

functions/bkg.fish

@@ -23,6 +23,8 @@
 # EXAMPLE
 #   bkg firefox
 function bkg --description 'Execute bkg'
+    __fish_help_header (status current-function) $argv; and return 0
+
     # Check if a command was provided as an argument.
     if test -z "$argv[1]"
         set -l c_head (set_color --bold cyan)

functions/fc.fish

@@ -24,6 +24,8 @@
 #   fc
 #   fc git
 function fc --description 'Edit and execute the last command (Bash-style fc)'
+    __fish_help_header (status current-function) $argv; and return 0
+
     set -l tmpfile (mktemp /tmp/fish_fc.XXXXXX).fish
 
     if count $argv >/dev/null

functions/hist.fish

@@ -17,6 +17,8 @@
 # EXAMPLE
 #   hist
 function hist --description 'Search fish history and put it in the prompt'
+    __fish_help_header (status current-function) $argv; and return 0
+
     # Opinionated guard (C4): integrations disabled
     if not __fish_config_op_enabled (status current-function)
         set -l c_err (set_color red)

functions/split.fish

@@ -29,6 +29,10 @@
 #   split
 #   split -v nvim README.md
 function split --description 'Run a command in a new terminal split'
+    # -h is --horizontal here (see this function's own ARGUMENTS),
+    # so only the long form may reach the renderer.
+    test "$argv[1]" = --help; and __fish_help_header (status current-function) --help; and return 0
+
     # Opinionated guard (C4): integrations disabled
     if not __fish_config_op_enabled (status current-function)
         set -l c_err (set_color red)

functions/spwin.fish

@@ -24,6 +24,8 @@
 # EXAMPLE
 #   spwin
 function spwin --wraps='~/.config/kitty/spawn-window.sh' --description 'spawn window in kitty or wezterm'
+    __fish_help_header (status current-function) $argv; and return 0
+
     # Opinionated guard (C4): integrations disabled
     if not __fish_config_op_enabled (status current-function)
         set -l c_err (set_color red)

functions/tab.fish

@@ -25,6 +25,8 @@
 # EXAMPLE
 #   tab
 function tab --description 'Spawn a new tab in the current terminal'
+    __fish_help_header (status current-function) $argv; and return 0
+
     # Opinionated guard (C4): integrations disabled
     if not __fish_config_op_enabled (status current-function)
         set -l c_err (set_color red)

functions/wake-lock.fish

@@ -22,6 +22,8 @@
 # EXAMPLE
 #   wake-lock rsync -avz src/ dest/
 function wake-lock --description 'Run a command while inhibiting system sleep'
+    __fish_help_header (status current-function) $argv; and return 0
+
     if test (count $argv) -eq 0
         set -l c_head (set_color --bold cyan)
         set -l c_cmd (set_color --bold)