fix: calendar disappeared for existing users

Shallow Object.assign on settings meant filterTags (new in 1.5.0) was
undefined for anyone with prior saved settings. Accessing .length on
undefined threw, killing the entire redraw before calendar could render.

- Defensive fallback: filterTags || []
- Deep merge on loadSettings for recentFiles, calendar, display

manifest.json

@@ -1,7 +1,7 @@
 {
 	"id": "waypoint-sidebar",
 	"name": "Waypoint Sidebar",
-	"version": "1.5.0",
+	"version": "1.5.1",
 	"minAppVersion": "0.16.3",
 	"description": "Calendar, recent files, and custom bookmarks sidebar.",
 	"author": "Olivier",