nixos/foot: only modify the prompt when running inside foot

Without this, these integration scripts will mess with the prompt even
when not running a shell inside of foot. This can break:

1. Terminals that don't understand these sequences (e.g., gnome-terminal
and likely other vte based terminals).
2. Anything that tries to parse the prompt (Emacs packages like
bash-completion).

This patch relies on the TERM variable (against upstream's
recommendation [1]) because:

1. Only Fish [2] has built-in support for querying things like
XTVERSION. Querying terminal features manually is non-trivial and
requires writing to STDOUT, which I'd like to avoid.

2. Even in Fish, this XTVERSION may only be queried after the first
prompt has been displayed ([2]), which is too late.

This patch does not explicitly check if the terminal is interactive as
the modified files are only sourced by interactive shells anyway.

[1]: https://codeberg.org/dnkl/foot#programmatically-checking-if-running-in-foot
[2]: https://fishshell.com/docs/current/cmds/status.html#status-terminal

fixes #374613

nixos/modules/programs/foot/bashrc

@@ -1,3 +1,8 @@
+case "$TERM" in
+  foot*) : ;;
+  *) return 0 ;;
+esac
+
 osc7_cwd() {
     local strlen=${#PWD}
     local encoded=""

nixos/modules/programs/foot/config.fish

@@ -1,3 +1,7 @@
+if ! string match -q "foot*" "$TERM"
+  return 0
+end
+
 function update_cwd_osc --on-variable PWD --description 'Notify terminals when $PWD changes'
     if status --is-command-substitution || set -q INSIDE_EMACS
         return

nixos/modules/programs/foot/zshrc

@@ -1,3 +1,8 @@
+case "$TERM" in
+  foot*) : ;;
+  *) return 0 ;;
+esac
+
 function osc7-pwd() {
     emulate -L zsh # also sets localoptions for us
     setopt extendedglob