feat(help): standardize colored --help output across functions

Add the established c_head/c_cmd/c_flag/c_dim/c_arg color scheme to
--help (or usage-on-error) output in play-media and 13 other functions
that lacked it or used an ad hoc scheme: bkg, detach, replay, p, y,
spark, wake-lock, open-url, repo-open, dng2avif, dockup, fish-deps
(__fish_deps_help), and scrub.

Also tweak the standard itself:
- c_cmd now uses plain `set_color --bold` instead of `--bold white`,
  so the command name adapts to the terminal's foreground instead of
  forcing white text that washes out on light-background themes.
  Applied across all functions already using the pattern.
- jobrunner's reset variable renamed from c_rst to c_reset to match
  the naming used everywhere else.

functions/play-media.fish

@@ -36,15 +36,23 @@
 #   play-media
 #   play-media --player mpv
 function play-media --description 'Pick audio/video files with fzf and play them'
+    set -l c_head (set_color --bold cyan)
+    set -l c_cmd (set_color --bold)
+    set -l c_flag (set_color yellow)
+    set -l c_dim (set_color brblack)
+    set -l c_reset (set_color normal)
+
     argparse h/help p/player= -- $argv
     or return 1
 
     if set -q _flag_help
-        echo "Usage: play-media [-p|--player <cmd>]"
-        echo "Pick audio/video files under the current directory with fzf and play them."
+        echo "$c_head""Usage:$c_reset $c_cmd""play-media$c_reset $c_flag""[-p|--player$c_reset $c_dim<cmd>$c_reset""$c_flag]$c_reset"
         echo
-        echo "  -p, --player <cmd>  Force a specific player command"
-        echo "  -h, --help          Show this help"
+        echo "  Pick audio/video files under the current directory with fzf and play them."
+        echo
+        echo "$c_head""Options:$c_reset"
+        echo "  $c_flag-p$c_reset, $c_flag--player$c_reset $c_dim<cmd>$c_reset  Force a specific player command"
+        echo "  $c_flag-h$c_reset, $c_flag--help$c_reset          Show this help"
         return 0
     end