feat(daily-prep): replace Plan-My-Day header icon with a stroked sun icon

Renders the new SVG faithfully via a stroked Path (PathIcon fills, so a
line-art icon would vanish). Renamed the button to "Plan My Day".

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

src/ClaudeDo.Localization/locales/de.json

@@ -67,7 +67,7 @@
     "enterKey": "ENTER",
     "notesPinnedRow": "Notizen (Tagesnotizen)",
     "clearDayTip": "Tag leeren",
-    "prepLogTip": "Vorbereitungs-Log",
+    "planMyDayTip": "Meinen Tag planen",
     "overdue": "ÜBERFÄLLIG",
     "tasks": "AUFGABEN",
     "clearCompletedTip": "Alle abgeschlossenen löschen",