feat: add waybar module for package update notifications

Add moonarch-waybar-updates script that checks for available updates
from both official repos (checkupdates) and AUR (paru -Qua). Uses a
cache mechanism to avoid excessive mirror hits while still detecting
freshly installed updates within 60 seconds.

defaults/bin/moonarch-waybar-updates

@@ -0,0 +1,68 @@
+#!/usr/bin/bash
+# ABOUTME: Waybar module that checks for available package updates with caching.
+# ABOUTME: Combines pacman repo updates (checkupdates) and AUR updates (paru -Qua).
+
+CACHE_DIR="${XDG_CACHE_HOME:-$HOME/.cache}/moonarch"
+CACHE_FILE="$CACHE_DIR/waybar-updates"
+PACMAN_DB="/var/lib/pacman/local"
+MAX_AGE=3600
+
+mkdir -p "$CACHE_DIR"
+
+needs_refresh() {
+    # No cache yet
+    [[ ! -f "$CACHE_FILE" ]] && return 0
+
+    # Pacman DB changed since last check (update was installed)
+    [[ "$PACMAN_DB" -nt "$CACHE_FILE" ]] && return 0
+
+    # Cache older than MAX_AGE
+    local age=$(( $(date +%s) - $(stat -c %Y "$CACHE_FILE") ))
+    [[ "$age" -ge "$MAX_AGE" ]] && return 0
+
+    return 1
+}
+
+if needs_refresh; then
+    repo_updates=$(checkupdates 2>/dev/null)
+    repo_count=0
+    if [[ -n "$repo_updates" ]]; then
+        repo_count=$(echo "$repo_updates" | wc -l)
+    fi
+
+    aur_updates=""
+    aur_count=0
+    if command -v paru &>/dev/null; then
+        aur_updates=$(paru -Qua 2>/dev/null)
+        if [[ -n "$aur_updates" ]]; then
+            aur_count=$(echo "$aur_updates" | wc -l)
+        fi
+    fi
+
+    total=$((repo_count + aur_count))
+
+    if [[ "$total" -eq 0 ]]; then
+        echo "" > "$CACHE_FILE"
+        exit 0
+    fi
+
+    # Build tooltip with package lists
+    tooltip=""
+    if [[ -n "$repo_updates" ]]; then
+        tooltip+="Repo ($repo_count):"$'\n'"$repo_updates"
+    fi
+    if [[ -n "$aur_updates" ]]; then
+        [[ -n "$tooltip" ]] && tooltip+=$'\n\n'
+        tooltip+="AUR ($aur_count):"$'\n'"$aur_updates"
+    fi
+
+    jq --compact-output -n \
+        --arg text "$total" \
+        --arg alt "has-updates" \
+        --arg tooltip "$tooltip" \
+        --arg class "has-updates" \
+        '{text: $text, alt: $alt, tooltip: $tooltip, class: $class}' > "$CACHE_FILE"
+fi
+
+# Output cached result (empty cache = no updates = module hidden)
+cat "$CACHE_FILE"