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/repo-open.fish

@@ -52,17 +52,23 @@
 # NOTES
 #   Typo abbreviation: open-repo (expands to repo-open on space/enter).
 function repo-open --description 'Open the origin remote of the current repo in a browser'
+    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_reset (set_color normal)
+
     argparse -X 0 h/help p/print r/root -- $argv
     or return 1
 
     if set -q _flag_help
-        echo "Usage: repo-open [-p|--print] [-r|--root]"
-        echo "Open the origin remote's web page for the current repo,"
-        echo "deep-linking to the current branch and sub-directory."
+        echo "$c_head""Usage:$c_reset $c_cmd""repo-open$c_reset $c_flag""[-p|--print] [-r|--root]$c_reset"
+        echo "  Open the origin remote's web page for the current repo,"
+        echo "  deep-linking to the current branch and sub-directory."
         echo
-        echo "  -p, --print  Print the URL instead of opening it"
-        echo "  -r, --root   Link to the repo root, ignoring the current sub-directory"
-        echo "  -h, --help   Show this help"
+        echo "$c_head""Options:$c_reset"
+        echo "  $c_flag-p$c_reset, $c_flag--print$c_reset  Print the URL instead of opening it"
+        echo "  $c_flag-r$c_reset, $c_flag--root$c_reset   Link to the repo root, ignoring the current sub-directory"
+        echo "  $c_flag-h$c_reset, $c_flag--help$c_reset   Show this help"
         return 0
     end