C0: blumeops-tasks — replace ambiguous due:+N with "Nd overdue"

The signed offset format read as "due in 5 days" rather than
"5 days overdue", causing misreads. Switch to self-explanatory
text: "5d overdue" / "due in 2d" / "due today".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mise-tasks/blumeops-tasks

@@ -189,7 +189,12 @@ def main() -> int:
         meta = []
         days = days_until_due(task)
         if days is not None:
-            meta.append(f"due:{days:+d}" if days != 0 else "due:today")
+            if days == 0:
+                meta.append("due today")
+            elif days > 0:
+                meta.append(f"{days}d overdue")
+            else:
+                meta.append(f"due in {-days}d")
         recurrence = recurrence_string(task)
         if recurrence:
             meta.append(f"↻ {recurrence}")