docs: add DEPENDENCIES sections to function doc headers

Documents what each function needs for full functionality -- other
repo functions it calls, and external CLI tools it uses or falls
back gracefully without (e.g. rm/trash, ls/eza+lsd) -- matching the
existing CLASSIFICATION convention's placement and the ~20 functions
that already carried this label.

Also broadens verify-manual.py's dependency-resolution check to
recognize this repo's other existence-check idioms (command -q,
command -v, which -- not just type -q) and dng2avif's dynamic
type -q $cmd loop, since several genuine dependencies (eza, lsd,
fastfetch, fd, ps, ...) are only ever guarded that way.

functions/kitty-logging.fish

@@ -7,6 +7,10 @@
 # COMPONENT
 #   logging/terminal-capture
 #
+# DEPENDENCIES
+#   kitty, __kitty_logging_dir, __kitty_logging_has_watcher,
+#   __kitty_logging_version
+#
 # CLASSIFICATION
 #   bypasses-shadow(grep,mkdir,rm)
 #