keep the shell templates together in scripts/setup

starship.toml, tmux.conf and zshrc side by side. tmux.conf and zshrc moved up out
of machine-setup/.

starship.toml could not have moved down to join them: the PLATFORM reads it, at
src/servers/os-user-shell.ts:34, to deploy to every member's Linux account. That
is a runtime path rather than an import, so moving it would have broken member
provisioning silently — no build error, members simply get no starship config.
So the templates collect where the shared one already had to be.

Left as a marker for tomorrow rather than resolved: there are now TWO zshrc
templates, this one for the owner and shell-skel/zshrc for members, while
starship.toml is deliberately one file for both. Either the owner needs different
shell config from a member or they should be the same file. tmux.conf has the
same question waiting, since it is going into provisioning too. Noted in the
zshrc header where whoever picks it up will be looking.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/setup/machine-setup/machine-setup.sh

@@ -2225,11 +2225,15 @@ if ! skip; then
       esac
     fi
 
-    # `tmux.conf`, no leading dot. It is a TEMPLATE in the repository, not a
-    # dotfile in a home directory, and the destination is increasingly
-    # ~/.config/tmux/tmux.conf — which has no dot either. Naming the source after
-    # a path it may not be installed to is how you end up reading the wrong file.
-    if [[ -r "$SCRIPT_DIR/tmux.conf" ]]; then
+    # scripts/setup/tmux.conf, one level up — the shell templates live together
+    # beside starship.toml, which has to be there because the PLATFORM reads it
+    # too (os-user-shell.ts, for every member's Linux account). Keeping them in
+    # one directory means "where do the dotfile templates live" has one answer.
+    #
+    # No leading dot on any of them: they are templates in a repository, not
+    # dotfiles in a home directory, and tmux's destination is increasingly
+    # ~/.config/tmux/tmux.conf, which has no dot either.
+    if [[ -r "$SCRIPT_DIR/../tmux.conf" ]]; then
       # Not always ~/.tmux.conf — see tmux_config_target. tmux 3.1+ prefers
       # ~/.config/tmux/tmux.conf, so writing the old path on a machine that has
       # the new one produces a file tmux never reads and a success message that
@@ -2240,7 +2244,7 @@ if ! skip; then
         echo "     Targeting the one it actually reads: ${TMUX_TARGET}"
       fi
       install -d -m 0755 -o "$USERNAME" -g "$(user_group)" "$(dirname "$TMUX_TARGET")"
-      install_config "$SCRIPT_DIR/tmux.conf" "$TMUX_TARGET" "$USERNAME" && RC=0 || RC=$?
+      install_config "$SCRIPT_DIR/../tmux.conf" "$TMUX_TARGET" "$USERNAME" && RC=0 || RC=$?
       case $RC in
         0) ok "tmux config installed — ${TMUX_TARGET}" ;;
         1) echo "     tmux config already matches (${TMUX_TARGET})" ;;