feat: add manual interval creation and inline entry editing

- Service: CreateInterval() validates same-day, end>start, day not closed
- Service: Update() now rejects edits on closed-day entries (ErrDayAlreadyClosed)
- Handler: POST /api/entries creates a completed interval with explicit times
- API client: entries.createInterval(startMs, endMs, note)
- Utils: parseTimeInput / toTimeInput helpers for HH:MM <-> unix ms
- Today page: '+ Add interval' form (time pickers + optional note)
- Today page: pencil button on each entry opens inline edit row (start/end/note)
- Tests: TestCreateInterval, TestCreateIntervalEndBeforeStart,
         TestCreateIntervalCrossesMidnight, TestUpdateRejectsClosedDay

internal/service/entry_service.go

@@ -176,6 +176,15 @@ func (s *EntryService) Update(ctx context.Context, id string, input UpdateEntryI
 		return nil, err
 	}
 
+	// Disallow editing entries that belong to a closed day.
+	closed, err := s.closedDays.GetByDayKey(ctx, e.DayKey)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return nil, err
+	}
+	if closed != nil {
+		return nil, ErrDayAlreadyClosed
+	}
+
 	if input.StartTime != nil {
 		e.StartTime = *input.StartTime
 		e.DayKey = s.dayKeyForMs(e.StartTime)
@@ -203,6 +212,50 @@ func (s *EntryService) Update(ctx context.Context, id string, input UpdateEntryI
 	return e, nil
 }
 
+// CreateIntervalInput holds fields for a manually created completed interval.
+type CreateIntervalInput struct {
+	StartTime int64
+	EndTime   int64
+	Note      string
+}
+
+// CreateInterval adds a completed interval with explicit start and end times.
+// Rules: same-day, end > start, day not closed, no currently running entry on that day (check running globally).
+func (s *EntryService) CreateInterval(ctx context.Context, input CreateIntervalInput) (*domain.Entry, error) {
+	if input.EndTime <= input.StartTime {
+		return nil, fmt.Errorf("end_time must be after start_time")
+	}
+
+	startDayKey := s.dayKeyForMs(input.StartTime)
+	endDayKey := s.dayKeyForMs(input.EndTime)
+	if startDayKey != endDayKey {
+		return nil, ErrCrossesMidnight
+	}
+
+	// Check day is not closed.
+	closed, err := s.closedDays.GetByDayKey(ctx, startDayKey)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return nil, err
+	}
+	if closed != nil {
+		return nil, ErrDayAlreadyClosed
+	}
+
+	nowMs := s.nowMs()
+	e := &domain.Entry{
+		ID:        uuid.New().String(),
+		StartTime: input.StartTime,
+		EndTime:   &input.EndTime,
+		Note:      input.Note,
+		DayKey:    startDayKey,
+		UpdatedAt: nowMs,
+	}
+	if err := s.entries.Create(ctx, e); err != nil {
+		return nil, err
+	}
+	return e, nil
+}
+
 // Delete soft-deletes an entry.
 func (s *EntryService) Delete(ctx context.Context, id string) error {
 	nowMs := s.nowMs()

internal/service/entry_service_test.go

@@ -2,6 +2,7 @@ package service_test
 
 import (
 	"context"
+	"errors"
 	"testing"
 	"time"
 
@@ -134,3 +135,98 @@ func TestListEntries(t *testing.T) {
 		t.Fatalf("expected 3 entries, got %d", len(entries))
 	}
 }
+
+func TestCreateInterval(t *testing.T) {
+	ctx := context.Background()
+	svc := newTestServices(t)
+
+	now := time.Now().UTC()
+	startMs := now.Add(-2 * time.Hour).UnixMilli()
+	endMs := now.Add(-1 * time.Hour).UnixMilli()
+
+	entry, err := svc.CreateInterval(ctx, service.CreateIntervalInput{
+		StartTime: startMs,
+		EndTime:   endMs,
+		Note:      "manual entry",
+	})
+	if err != nil {
+		t.Fatalf("CreateInterval: %v", err)
+	}
+	if entry.EndTime == nil {
+		t.Fatal("expected EndTime to be set")
+	}
+	if *entry.EndTime != endMs {
+		t.Errorf("expected EndTime %d, got %d", endMs, *entry.EndTime)
+	}
+	if entry.Note != "manual entry" {
+		t.Errorf("expected note 'manual entry', got %q", entry.Note)
+	}
+}
+
+func TestCreateIntervalEndBeforeStart(t *testing.T) {
+	ctx := context.Background()
+	svc := newTestServices(t)
+
+	now := time.Now().UTC().UnixMilli()
+	_, err := svc.CreateInterval(ctx, service.CreateIntervalInput{
+		StartTime: now,
+		EndTime:   now - 1000,
+	})
+	if err == nil {
+		t.Fatal("expected error for end_time before start_time")
+	}
+}
+
+func TestCreateIntervalCrossesMidnight(t *testing.T) {
+	ctx := context.Background()
+	svc := newTestServices(t)
+
+	yesterday := time.Now().UTC().Add(-24 * time.Hour)
+	startMs := time.Date(yesterday.Year(), yesterday.Month(), yesterday.Day(), 23, 0, 0, 0, time.UTC).UnixMilli()
+	endMs := time.Now().UTC().Add(time.Hour).UnixMilli()
+
+	_, err := svc.CreateInterval(ctx, service.CreateIntervalInput{
+		StartTime: startMs,
+		EndTime:   endMs,
+	})
+	if err == nil {
+		t.Fatal("expected ErrCrossesMidnight")
+	}
+	if !errors.Is(err, service.ErrCrossesMidnight) {
+		t.Fatalf("expected ErrCrossesMidnight, got %v", err)
+	}
+}
+
+func TestUpdateRejectsClosedDay(t *testing.T) {
+	ctx := context.Background()
+
+	db, err := store.Open(":memory:")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	entryStore := store.NewEntryStore(db)
+	closedDayStore := store.NewClosedDayStore(db)
+	settingsStore := store.NewSettingsStore(db)
+	tz, _ := time.LoadLocation("UTC")
+	svc := service.NewEntryService(entryStore, closedDayStore, settingsStore, tz)
+	daySvc := service.NewDayService(entryStore, closedDayStore, settingsStore, tz)
+
+	entry, _ := svc.Start(ctx, "")
+	svc.Stop(ctx)
+
+	today := time.Now().UTC().Format("2006-01-02")
+	if _, err := daySvc.CloseDay(ctx, today); err != nil {
+		t.Fatalf("CloseDay: %v", err)
+	}
+
+	note := "should fail"
+	_, err = svc.Update(ctx, entry.ID, service.UpdateEntryInput{Note: &note})
+	if err == nil {
+		t.Fatal("expected error updating entry in closed day")
+	}
+	if !errors.Is(err, service.ErrDayAlreadyClosed) {
+		t.Fatalf("expected ErrDayAlreadyClosed, got %v", err)
+	}
+}