feat(todo): reminders at a time of their own planned and set in a task's sheet, durations in its date sheet

planReminders plans each reminder at a time of its own of an open task,
whatever its date, under an ID of its own; the notification says
"Reminder" for a task without a time. The task's sheet always has its
reminders' row: those before its time where it has one, those at a time
of their own each with its remove button and "Remind at a time" (a day,
then a time), the permission asked as a first one is chosen. The date
sheet sets a duration once there is a time (none, 15 minutes to 4
hours, as Todoist's), a time cleared taking it with it. Recorded as
ADR 0033, D18 (the developer's, 3 Nov 2026).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/todo/halkyon_todo_flutter/lib/l10n/app_en.arb

@@ -343,6 +343,39 @@
   "remindersChannel": "Task reminders",
   "remindersNotAllowed": "Notifications are off for Halkyon Todo: reminders show once you allow them in the system's settings.",
   "remindersOnThisDevice": "Reminders come on each of your devices that opens your tasks.",
+  "reminderBody": "Reminder",
+  "remindersAtTimes": "At a time of their own",
+  "reminderAddTime": "Remind at a time",
+  "reminderRemove": "Remove the reminder",
+  "durationTitle": "Duration",
+  "durationNone": "No duration",
+  "durationHours": "{hours} h",
+  "@durationHours": {
+    "placeholders": {
+      "hours": {
+        "type": "int"
+      }
+    }
+  },
+  "durationMinutes": "{minutes} min",
+  "@durationMinutes": {
+    "placeholders": {
+      "minutes": {
+        "type": "int"
+      }
+    }
+  },
+  "durationHoursMinutes": "{hours} h {minutes} min",
+  "@durationHoursMinutes": {
+    "placeholders": {
+      "hours": {
+        "type": "int"
+      },
+      "minutes": {
+        "type": "int"
+      }
+    }
+  },
   "weekPrevious": "Previous week",
   "weekNext": "Following week",
   "searchTitle": "Search",