feat(help): header-driven --help for development functions, plus the wiring guard

bd-pull, branch, check_fish_deps, claude-docs, claude-pr, fast, poke, qr
and parur take the standard call site. fish-deps instead routes -h/--help
to its existing __fish_deps_help, which previously answered only via the
unknown-subcommand path, printing "Unknown subcommand: --help" and
exiting 1.

This completes the 40 conversions and lands
test_every_user_facing_function_has_help -- acceptance criterion 6, the
check that fails when a new user-facing function ships without help. It
was developed red against the pre-conversion tree and reported exactly
the 40 names of the design's CONVERT table:

    bd-pull bkg branch check_fish_deps claude-docs claude-pr cleanup
    fast fc fish-deps fzf-update gip gip4 gip6 hist lD ld limine-edit
    lock lsr lss lstree lt ltr lx parur poke ports qr sbver screensleep
    split spwin steam-dl sudo-toggle swapstat tab tmux-clean upgrade
    wake-lock

each as "<name>: no -h/--help handling and not in $__help_exempt", with
the guard exiting 1. The count fell 40 -> 32 -> 24 -> 17 -> 10 -> 0
across the conversion commits. It is committed green so every commit on
this branch passes the suite.

$__help_exempt is the single machine-readable exemption record; a second
assertion fails if an exempt name stops being a published function, so a
rename or deletion upstream cannot silently exempt nothing.

functions/fish-deps.fish

@@ -66,6 +66,13 @@ function fish-deps --description 'Manage fish shell dependencies'
             _fish_deps_status
         case install
             _fish_deps_install $flags
+        case -h --help
+            # Reuse the existing menu rather than the header renderer: it
+            # is richer, and it is already the text the unknown-subcommand
+            # path prints. Previously --help fell into `case '*'` and
+            # exited 1 with "Unknown subcommand: --help".
+            __fish_deps_help
+            return 0
         case update
             _fish_deps_update
         case sync