Set TERM=dumb fallback in devx env script for CI/container environments

GHC's Makefile unconditionally calls `tput bold` and `tput sgr0`
(lines 217-218) which fail with "No value for $TERM and no -T
specified" when TERM is unset. This happens in CI runners and
containers where no terminal is attached.

Set TERM to "dumb" as a fallback after sourcing setup.sh so ncurses
tools like tput degrade gracefully instead of erroring.

Author: angerman

flake.nix

@@ -383,6 +383,10 @@
                   [ -n "$_DEVX_HOME" ] && export HOME="$_DEVX_HOME"
                   unset _DEVX_HOME
 
+                  # Set TERM=dumb if not already set so tput and other
+                  # ncurses tools don't fail in CI/container environments.
+                  export TERM="''${TERM:-dumb}"
+
                   # Shell hook from mkShell
                   ${shellHook}