fix: address audit findings — nil pointers, timezone bug, dead code, tests, README

- Fix nil pointer dereference in clock.go (guard GetOrCreateSettings and
  GetOrCreateRPGStats errors before accessing fields)
- Fix timezone bug in handleSetBreakMsg (was using system time.Now()
  instead of user's configured timezone)
- Remove dead code: sendExportMonthPicker (unused wrapper)
- Simplify xpForWorkSeconds (xpPerSecond=1, inline to just return sec)
- Extract computeStreakFromDates as pure testable function from
  recalcAggregates; add 6 tests covering empty, current, gaps,
  no-today, long streak, longest-not-current edge cases
- Update README with full feature documentation: RPG, League, Salary,
  Burnout, Work Types, Inline History Editing, all missing commands

internal/bot/clock.go

@@ -64,24 +64,26 @@ func (h *Handler) clockOut(chatID int64) (string, error) {
 	text := fmt.Sprintf("clocked out at %s", now.Format(TimeLayout))
 
 	// Award XP and update streaks if RPG enabled
-	st, _ := h.DB.GetOrCreateSettings(user.ID)
-	if st.RPGEnabled {
+	st, err := h.DB.GetOrCreateSettings(user.ID)
+	if err == nil && st.RPGEnabled {
 		sessionWork := now.Unix() - last.OccurredAt
 		today := now.Format(DateLayout)
 		isWeekend := now.Weekday() == time.Saturday || now.Weekday() == time.Sunday
 
-		stats, _ := h.DB.GetOrCreateRPGStats(user.ID)
-		h.updateStreak(stats, user.ID, today)
-		xp, leveledUp, newLevel, _ := h.computeAndAwardXP(stats, user.ID, sessionWork, stats.CurrentStreak, today)
-		totalHours := float64(stats.TotalWorkSeconds) / secondsPerHour
-		unlocked := h.checkAchievements(user.ID, stats, sessionWork, today, isWeekend, totalHours)
+		stats, err := h.DB.GetOrCreateRPGStats(user.ID)
+		if err == nil {
+			h.updateStreak(stats, user.ID, today)
+			xp, leveledUp, newLevel, _ := h.computeAndAwardXP(stats, user.ID, sessionWork, stats.CurrentStreak, today)
+			totalHours := float64(stats.TotalWorkSeconds) / secondsPerHour
+			unlocked := h.checkAchievements(user.ID, stats, sessionWork, today, isWeekend, totalHours)
 
-		text += fmt.Sprintf("\n\n+%d XP (Lv.%d)", xp, newLevel)
-		if leveledUp {
-			text += "\nLevel up!"
-		}
-		for _, a := range unlocked {
-			text += fmt.Sprintf("\nAchievement: %s", a)
+			text += fmt.Sprintf("\n\n+%d XP (Lv.%d)", xp, newLevel)
+			if leveledUp {
+				text += "\nLevel up!"
+			}
+			for _, a := range unlocked {
+				text += fmt.Sprintf("\nAchievement: %s", a)
+			}
 		}
 	}