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/recurrence_test.go

@@ -0,0 +1,97 @@
+package storage
+
+import (
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/sandrodach/mindsift/internal/domain"
+)
+
+func TestNextDueDate(t *testing.T) {
+	today := time.Date(2026, 10, 29, 15, 0, 0, 0, time.UTC)
+	cases := []struct{ due, rule, want string }{
+		{"2026-10-30", "daily", "2026-10-31"},
+		{"2026-10-30", "weekly", "2026-11-06"},
+		{"2026-01-31", "monthly", "2026-02-28"},
+		{"2026-03-15", "monthly", "2026-04-15"},
+		{"2028-02-29", "yearly", "2029-02-28"},
+		{"", "weekly", "2026-11-05"},
+	}
+	for _, c := range cases {
+		if got := NextDueDate(c.due, c.rule, today); got != c.want {
+			t.Errorf("NextDueDate(%q, %s) = %s, want %s", c.due, c.rule, got, c.want)
+		}
+	}
+}
+
+func TestRepeatingTaskSpawnsItsSuccessorOnce(t *testing.T) {
+	store, err := NewStore(filepath.Join(t.TempDir(), "recur.db"))
+	if err != nil {
+		t.Fatalf("NewStore: %v", err)
+	}
+	defer store.Close()
+	openSharing(t, store)
+	anna, _ := store.CreateUser("anna@example.com", "hash", "Anna", "member")
+	ben, _ := store.CreateUser("ben@example.com", "hash", "Ben", "member")
+	tl, _ := store.CreateTaskList(anna.ID, "", "", "Haushalt", "", "")
+	_, _ = store.AddTaskListShare(tl.ID, "user", ben.ID, "editor", anna.ID)
+
+	var pushed []*domain.Thought
+	store.OnTaskCreated = func(th *domain.Thought) { pushed = append(pushed, th) }
+
+	task, _ := store.CreateThoughtWithDetails(anna.ID, "Müll rausbringen #haushalt", "high", "manual", "2026-11-02", tl.ID, "todo", "Gelbe Tonne")
+	_, _ = store.UpdateThoughtTriage(anna.ID, task.ID, "keep", "task", "", "2026-11-02", tl.ID)
+	subs := []domain.SubTask{{ID: "s1", Title: "Tüten", IsCompleted: true}}
+	_, _ = store.UpdateThoughtDetails(anna.ID, task.ID, nil, nil, nil, nil, nil, nil, nil, &subs, nil)
+	_, _ = store.SetTaskAssignees(anna.ID, task.ID, []string{ben.ID})
+	if err := store.SetTaskRecurrence(anna.ID, task.ID, "weekly"); err != nil {
+		t.Fatalf("SetTaskRecurrence: %v", err)
+	}
+	if err := store.SetTaskRecurrence(anna.ID, task.ID, "stündlich"); err == nil {
+		t.Errorf("unknown rule must be rejected")
+	}
+
+	done := true
+	if _, err := store.UpdateThoughtDetails(ben.ID, task.ID, nil, &done, nil, nil, nil, nil, nil, nil, nil); err != nil {
+		t.Fatalf("complete: %v", err)
+	}
+	if len(pushed) != 1 {
+		t.Fatalf("expected one successor pushed live, got %d", len(pushed))
+	}
+	next := pushed[0]
+	if next.Content != "Müll rausbringen #haushalt" || next.Priority != "high" || next.Notes != "Gelbe Tonne" ||
+		next.DueDate != "2026-11-09" || next.Recurrence != "weekly" || next.IsCompleted || next.TaskListID != tl.ID ||
+		next.KanbanStatus != "todo" || len(next.Subtasks) != 1 || next.Subtasks[0].IsCompleted ||
+		len(next.Assignees) != 1 || next.Assignees[0] != ben.ID || next.UserID != anna.ID {
+		t.Errorf("successor wrong: %+v", next)
+	}
+	if orig, _ := store.GetThoughtByID(anna.ID, task.ID); !orig.IsCompleted {
+		t.Errorf("the completed task stays completed for the history")
+	}
+
+	// Re-opening and completing again creates no duplicate
+	open := false
+	_, _ = store.UpdateThoughtDetails(anna.ID, task.ID, nil, &open, nil, nil, nil, nil, nil, nil, nil)
+	_, _ = store.UpdateThoughtDetails(anna.ID, task.ID, nil, &done, nil, nil, nil, nil, nil, nil, nil)
+	if len(pushed) != 1 {
+		t.Fatalf("re-completing must not spawn again, got %d successors", len(pushed))
+	}
+
+	// Dragging the successor into "done" on the Kanban board repeats as well
+	status := "done"
+	if err := store.ReorderTasks(tl.ID, []domain.ThoughtReorderItem{{ID: next.ID, SortOrder: 0, KanbanStatus: &status}}); err != nil {
+		t.Fatalf("ReorderTasks: %v", err)
+	}
+	if len(pushed) != 2 || pushed[1].DueDate != "2026-11-16" {
+		t.Fatalf("Kanban completion should spawn the next week, got %+v", pushed)
+	}
+
+	// A task without rule never repeats
+	plain, _ := store.CreateThoughtWithDetails(anna.ID, "Einmalig", "normal", "manual", "", tl.ID, "todo", "")
+	_, _ = store.UpdateThoughtTriage(anna.ID, plain.ID, "keep", "task", "", "", tl.ID)
+	_, _ = store.UpdateThoughtDetails(anna.ID, plain.ID, nil, &done, nil, nil, nil, nil, nil, nil, nil)
+	if len(pushed) != 2 {
+		t.Errorf("non-repeating task must not spawn")
+	}
+}