Replace dunst with swaync for fractional scaling support

Dunst lacks wp_fractional_scale_v1, causing jagged font rendering
on external monitors in mixed-DPI setups (laptop 2.5x + externals 1x).
swaync (GTK4) handles fractional scaling natively.

Style based on catppuccin/swaync with Lavender accent.

defaults/xdg/swaync/config.json

@@ -0,0 +1,46 @@
+{
+    "$schema": "/etc/xdg/swaync/configSchema.json",
+
+    "positionX": "right",
+    "positionY": "top",
+    "layer": "overlay",
+    "control-center-layer": "top",
+    "cssPriority": "application",
+
+    "notification-window-width": 300,
+    "notification-icon-size": 64,
+    "notification-body-image-height": 100,
+    "notification-body-image-width": 200,
+
+    "timeout": 10,
+    "timeout-low": 5,
+    "timeout-critical": 0,
+
+    "fit-to-screen": true,
+    "control-center-margin-top": 15,
+    "control-center-margin-bottom": 15,
+    "control-center-margin-right": 15,
+    "control-center-width": 400,
+    "control-center-height": 600,
+
+    "notification-2fa-action": true,
+    "notification-inline-replies": false,
+    "notification-visibility": {},
+
+    "widgets": [
+        "title",
+        "dnd",
+        "notifications"
+    ],
+
+    "widget-config": {
+        "title": {
+            "text": "Notifications",
+            "clear-all-button": true,
+            "button-text": "Clear All"
+        },
+        "dnd": {
+            "text": "Do Not Disturb"
+        }
+    }
+}