install.sh: use 'nix profile add' instead of deprecated 'install' alias in nixos_profile_install — the binary already used 'add' (exec.zig) but the installer still printed warning: 'install' is a deprecated alias for 'add'; update the section header and failure message to match; sh -n clean

@@ -151,7 +151,7 @@151151   return 0152152 }153153 154-# ── NixOS: nix profile install (primary) ─────────────────────────────────────154+# ── NixOS: nix profile add (primary) ─────────────────────────────────────────155155 156156 nixos_profile_install() {157157   have nix || return 1@@ -160,11 +160,13 @@160160   # Tarball flakes are fetched read-only into the store, so nix cannot persist161161   # a freshly-resolved flake.lock and aborts with "cannot write modified lock162162   # file". --no-write-lock-file resolves inputs in memory without writing.163-  if nix profile install --no-write-lock-file "${FLAKE_URL}#nina"; then163+  # `add` is the current verb; `install` is a deprecated alias that prints a164+  # warning on modern nix. Mirrors exec.zig profileInstall.165+  if nix profile add --no-write-lock-file "${FLAKE_URL}#nina"; then164166     return 0165167   fi166168   blank167-  say "nix profile install failed. Common causes:"169+  say "nix profile add failed. Common causes:"168170   say "  flakes not enabled — add to /etc/nix/nix.conf or ~/.config/nix/nix.conf:"169171   say "    experimental-features = nix-command flakes"170172   say "  once nina is installed: nina setup enables this automatically"