feat(tasks): repeating tasks (daily, weekly, monthly, yearly)

- recurrence on tasks, set in the detail dialog; 🔁 on rows and Kanban cards
- Completing a repeating task (detail, list, Kanban drag to done, note
  checkbox) creates the next one: title, tags, priority, notes, list,
  assignees and rule copied, subtasks reset, first open column, due date
  one interval later (month end clamped); pushed live as TASK_CREATED
- Each task spawns at most once (re-open + complete makes no duplicate)
- Export/import keep the rule (Obsidian Tasks "🔁 every week", JSON field)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/export_markdown.go

@@ -118,6 +118,9 @@ func (s *Store) writeVaultLists(zw *zip.Writer, userID string, names *vaultNames
 	return nil
 }
 
+// Obsidian Tasks writes repeat rules as "🔁 every week"
+var recurrenceEvery = map[string]string{"daily": "day", "weekly": "week", "monthly": "month", "yearly": "year"}
+
 // taskMarkdownLine writes a task in the format of the Obsidian Tasks plugin (📅 due date, ⏫/🔺 priority)
 // with its subtasks and notes indented below.
 func taskMarkdownLine(t domain.Thought) string {
@@ -134,6 +137,9 @@ func taskMarkdownLine(t domain.Thought) string {
 	case "low":
 		line += " 🔽"
 	}
+	if every, ok := recurrenceEvery[t.Recurrence]; ok {
+		line += " 🔁 every " + every
+	}
 	if t.DueDate != "" {
 		line += " 📅 " + t.DueDate
 	}