fix(theme): surface partial-apply failures instead of swallowing them

nomarchy-theme-set chains six optional "tell each app the theme changed"
steps. Each used `command -v X && X || true`, which collapsed two very
different outcomes into the same silent path:

  - X isn't installed -> skip (correct, expected, fine)
  - X exists but returned non-zero -> skip (wrong - user just got a
    half-applied theme with zero feedback about which app didn't refresh)

Replaced the inline guards with a small helper that distinguishes
absent from failed and accumulates real failures into a list. At the
end of the run, if anything failed, we notify-send a single message
naming the apps that didn't refresh ("Did not refresh: Waybar, btop")
and echo the same to stderr. The theme apply itself still completes -
we don't abort the chain on one failure - so the user gets the partial
benefit AND the diagnostic.

Same pattern as the waybar SIGUSR2 fix (386da51): make the hot path
loud about real problems while staying quiet about expected
no-installed states.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

themes/engine/scripts/nomarchy-theme-set

@@ -51,25 +51,55 @@ nomarchy-env-update
 
 nomarchy-theme-set-templates
 
+# Run the chain of "tell each app the theme changed" steps. Each step is
+# optional — the corresponding helper might not be installed, the service
+# might not be running, the user might not use Obsidian. Skipping is fine;
+# what we don't want is a step that EXISTS, fails for a real reason, and
+# leaves the user with a half-applied theme + no idea why. Collect every
+# real failure into _theme_set_fails and surface them in one notify-send
+# at the end so the user knows exactly what didn't refresh.
+_theme_set_fails=()
+
+_theme_set_try() {
+    local label="$1"; shift
+    # First arg after label is the command to test for existence.
+    # `systemctl` always exists on a NixOS system, so we let it through
+    # and rely on its own exit code to decide skip vs fail.
+    if [[ "$1" != "systemctl" ]] && ! command -v "$1" >/dev/null 2>&1; then
+        return 0   # not installed → silently skip
+    fi
+    if ! "$@" >/dev/null 2>&1; then
+        _theme_set_fails+=("$label")
+    fi
+}
+
 # Walker reads its CSS via @import of ~/.config/nomarchy/current/theme/apps/walker/style.css,
 # and waybar's shared fallback style does the same with waybar.css. HM's sd-switch
 # only restarts services whose unit *definition* changed, so when only the imported
 # file's contents change, neither gets reloaded. Restart them explicitly.
-command -v nomarchy-restart-walker >/dev/null 2>&1 && nomarchy-restart-walker || true
-command -v nomarchy-restart-waybar >/dev/null 2>&1 && nomarchy-restart-waybar || true
+_theme_set_try "Walker"  nomarchy-restart-walker
+_theme_set_try "Waybar"  nomarchy-restart-waybar
 
 # Hot-reload long-running TUIs / agents that read their colors from
 # the active-theme symlink and would otherwise stay on the old palette
 # until the user restarts them by hand.
-command -v nomarchy-restart-btop     >/dev/null 2>&1 && nomarchy-restart-btop     || true
-command -v nomarchy-restart-opencode >/dev/null 2>&1 && nomarchy-restart-opencode || true
+_theme_set_try "btop"     nomarchy-restart-btop
+_theme_set_try "opencode" nomarchy-restart-opencode
 
 # Sync palette into Obsidian vaults (no-op when the user has no Obsidian
 # config or no obsidian.css template in the active theme).
-command -v nomarchy-theme-set-obsidian >/dev/null 2>&1 && nomarchy-theme-set-obsidian || true
+_theme_set_try "Obsidian" nomarchy-theme-set-obsidian
 
 # Reload the wallpaper — its ExecStart path is stable (~/.config/nomarchy/current/background)
 # so sd-switch does not detect a unit change when only the symlink target moves.
-systemctl --user restart nomarchy-wallpaper.service 2>/dev/null || true
+_theme_set_try "wallpaper" systemctl --user restart nomarchy-wallpaper.service
+
+if (( ${#_theme_set_fails[@]} > 0 )); then
+    if command -v notify-send >/dev/null 2>&1; then
+        notify-send -u normal "Theme applied with warnings" \
+            "Did not refresh: $(IFS=', '; echo "${_theme_set_fails[*]}")"
+    fi
+    echo "Warning: failed to refresh: ${_theme_set_fails[*]}" >&2
+fi
 
 nomarchy-hook theme-set "$THEME_NAME"