rename the tmux template to tmux.conf, no leading dot

It is a template in the repository, not a dotfile in a home directory — and the
destination it is increasingly installed to, ~/.config/tmux/tmux.conf, has no dot
either. Naming the source after a path it may not be written to is how the wrong
file gets read.

The two remaining dotted references are correct and stay: they name the
DESTINATION ~/.tmux.conf, which does have a dot when that is where tmux looks.

.setup-answers and .setup-progress keep theirs too. They are runtime state in a
directory, not templates.

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

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

@@ -2225,7 +2225,11 @@ if ! skip; then
       esac
     fi
 
-    if [[ -r "$SCRIPT_DIR/.tmux.conf" ]]; then
+    # `tmux.conf`, no leading dot. It is a TEMPLATE in the repository, not a
+    # dotfile in a home directory, and the destination is increasingly
+    # ~/.config/tmux/tmux.conf — which has no dot either. Naming the source after
+    # a path it may not be installed to is how you end up reading the wrong file.
+    if [[ -r "$SCRIPT_DIR/tmux.conf" ]]; then
       # 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
@@ -2236,7 +2240,7 @@ 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})" ;;