make.tcl: restore 'shell' command guard deleted by projectversion edit

The projectversion commit accidentally removed the
'if {$::punkboot::command eq "shell"} {' guard line, orphaning the
shell command body (package require punk/repl, repl::start) at top-level
scope. This broke every command whose if-block lives after line 1942
(vfscommonupdate, vendorupdate, bin, project, modules, libs, packages,
vfs) — they would hit the orphaned shell body and attempt to start a
REPL instead of running their intended function.

No behaviour change beyond restoring the guard; diff vs pre-projectversion
make.tcl is now purely additive.

Assisted-by: harness=opencode; primary-model=openrouter/z-ai/glm-5.2; api-location=openrouter.ai

src/make.tcl

@@ -1939,6 +1939,8 @@ if {$::punkboot::command eq "projectversion"} {
     puts stdout $sep
     exit 0
 }
+
+if {$::punkboot::command eq "shell"} {
     package require struct::list
     package require punk
     package require punk::repl