refactor: eliminate store bypass and fix GetLastEvent style

- Add GetDistinctEventDates, UpdateEventWorkType, UpdateEventTime,
  DeleteEvent, GetEventByID store methods to calendar.go
- Replace all 5 raw h.DB.DB().Exec/Query calls with proper store methods
- Remove unused database/sql import from calendar.go
- Rewrite GetLastEvent to use QueryRow instead of Query+manual iteration
  (fixing row-vs-rows naming issue; removing rows.Close boilerplate)
- Add errors import to store.go for errors.Is

internal/db/store.go

@@ -4,6 +4,7 @@ package db
 import (
 	"database/sql"
 	"embed"
+	"errors"
 	"fmt"
 	"log/slog"
 	"time"
@@ -945,29 +946,77 @@ func (s *Store) CreateEvent(userID int64, dayID int64, eventType string, workTyp
 	return err
 }
 
+// GetDistinctEventDates returns distinct dates from the days table on which the user has events within range.
+func (s *Store) GetDistinctEventDates(userID int64, startDate, endDate string) ([]string, error) {
+	rows, err := s.db.Query(
+		"SELECT DISTINCT d.date FROM days d JOIN events e ON e.day_id = d.id WHERE d.user_id=? AND d.date >= ? AND d.date <= ? ORDER BY d.date",
+		userID, startDate, endDate,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var dates []string
+	for rows.Next() {
+		var d string
+		if err := rows.Scan(&d); err != nil {
+			return nil, err
+		}
+		dates = append(dates, d)
+	}
+	return dates, rows.Err()
+}
+
+// UpdateEventWorkType sets the work type for an event.
+func (s *Store) UpdateEventWorkType(eventID, workTypeID int64) error {
+	_, err := s.db.Exec("UPDATE events SET work_type_id=? WHERE id=?", workTypeID, eventID)
+	return err
+}
+
+// UpdateEventTime sets the occurred_at timestamp for an event.
+func (s *Store) UpdateEventTime(eventID, occurredAt int64) error {
+	_, err := s.db.Exec("UPDATE events SET occurred_at=? WHERE id=?", occurredAt, eventID)
+	return err
+}
+
+// DeleteEvent removes an event by ID.
+func (s *Store) DeleteEvent(eventID int64) error {
+	_, err := s.db.Exec("DELETE FROM events WHERE id=?", eventID)
+	return err
+}
+
+// GetEventByID returns a single event scoped to a user.
+func (s *Store) GetEventByID(eventID, userID int64) (*Event, error) {
+	row := s.db.QueryRow(
+		"SELECT id, user_id, day_id, event_type, work_type_id, occurred_at, note, created_at FROM events WHERE id=? AND user_id=?",
+		eventID, userID,
+	)
+	var e Event
+	var wt sql.NullInt64
+	if err := row.Scan(&e.ID, &e.UserID, &e.DayID, &e.EventType, &wt, &e.OccurredAt, &e.Note, &e.CreatedAt); err != nil {
+		return nil, err
+	}
+	if wt.Valid {
+		e.WorkTypeID = &wt.Int64
+	}
+	return &e, nil
+}
+
 // GetLastEvent returns the most recent event for the user, ordered by occurrence time.
 func (s *Store) GetLastEvent(userID int64) (*Event, error) {
-	row, err := s.db.Query(`
+	row := s.db.QueryRow(`
 		SELECT id, user_id, day_id, event_type, work_type_id, occurred_at, note, created_at
 		FROM events
 		WHERE user_id = ?
 		ORDER BY occurred_at DESC
 		LIMIT 1
 	`, userID)
-	if err != nil {
-		return nil, err
-	}
-	defer func() {
-		if err := row.Close(); err != nil {
-			slog.Warn("GetLastEvent: row.Close failed", "error", err)
-		}
-	}()
-	if !row.Next() {
-		return nil, sql.ErrNoRows
-	}
 	var e Event
 	var wt sql.NullInt64
 	if err := row.Scan(&e.ID, &e.UserID, &e.DayID, &e.EventType, &wt, &e.OccurredAt, &e.Note, &e.CreatedAt); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, sql.ErrNoRows
+		}
 		return nil, err
 	}
 	if wt.Valid {