refactor: split handlers.go into 5 files, redesign export month picker, pad calendar rows, improve comments

- Split 1571-line handlers.go into: handlers.go (core), clock.go, settings.go, calendar.go, report.go
- Redesigned export month picker: year navigation + 12-month grid instead of prev/next month
- Fixed calendar last row: pad remaining cells with empty buttons to ensure 7 columns
- Added Go doc comments across all files (dateutil.go, totals.go, store.go, main.go, webhook.go)

internal/bot/clock.go

@@ -0,0 +1,111 @@
+package bot
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+)
+
+// clockIn records a clock-in event for today.
+// Returns the formatted time or an error if already clocked in today.
+func (h *Handler) clockIn(chatID int64) (string, error) {
+	user, day, err := h.getUserToday(chatID)
+	if err != nil {
+		return "", err
+	}
+
+	last, err := h.DB.GetLastEvent(user.ID)
+	if err != nil && err != sql.ErrNoRows {
+		return "", err
+	}
+
+	if last != nil && last.EventType == "in" {
+		loc := loadLocation(user.Timezone)
+		now := time.Now().In(loc)
+		lastTime := time.Unix(last.OccurredAt, 0).In(loc)
+		if lastTime.Format("2006-01-02") == now.Format("2006-01-02") {
+			return "", errors.New("already clocked in")
+		}
+	}
+
+	loc := loadLocation(user.Timezone)
+	now := time.Now().In(loc)
+	wt := day.CurrentWorkTypeID
+	if err := h.DB.CreateEvent(user.ID, day.ID, "in", &wt, now.Unix(), ""); err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("clocked in at %s", now.Format("15:04")), nil
+}
+
+// clockOut records a clock-out event for today.
+// Returns the formatted time or an error if not clocked in.
+func (h *Handler) clockOut(chatID int64) (string, error) {
+	user, day, err := h.getUserToday(chatID)
+	if err != nil {
+		return "", err
+	}
+	last, err := h.DB.GetLastEvent(user.ID)
+	if err != nil {
+		return "", err
+	}
+	if last == nil {
+		return "", errors.New("no clock-in found — start with /clockin first")
+	}
+	if last.EventType == "out" {
+		return "", errors.New("already clocked out")
+	}
+	loc := loadLocation(user.Timezone)
+	now := time.Now().In(loc)
+	if err := h.DB.CreateEvent(user.ID, day.ID, "out", nil, now.Unix(), ""); err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("clocked out at %s", now.Format("15:04")), nil
+}
+
+// dayOff toggles today as a day off.
+func (h *Handler) dayOff(chatID int64) (string, error) {
+	user, day, err := h.getUserToday(chatID)
+	if err != nil {
+		return "", err
+	}
+	if day.IsDayOff {
+		if err := h.DB.RemoveDayOff(user.ID, day.Date); err != nil {
+			return "", err
+		}
+		return "day off removed", nil
+	}
+	if err := h.DB.SetDayOff(user.ID, day.Date, ""); err != nil {
+		return "", err
+	}
+	return "today marked as day off", nil
+}
+
+// report returns today's work summary via buildDailyReport.
+func (h *Handler) report(chatID int64) (string, error) {
+	user, day, err := h.getUserToday(chatID)
+	if err != nil {
+		return "", err
+	}
+	events, err := h.DB.EventsForDayByDayID(day.ID)
+	if err != nil {
+		return "", err
+	}
+	return h.buildDailyReport(user, day, events), nil
+}
+
+// toggleReport enables or disables the automatic daily report.
+func (h *Handler) toggleReport(chatID int64) (string, error) {
+	user, err := h.getOrCreateUser(chatID)
+	if err != nil {
+		return "", err
+	}
+	user.ReportEnabled = !user.ReportEnabled
+	if err := h.DB.UpdateUser(user); err != nil {
+		return "", err
+	}
+	if user.ReportEnabled {
+		return "daily report enabled", nil
+	}
+	return "daily report disabled", nil
+}