fix: currency validation, league mobile layout, settings 2-col, burnout ratio, add setusername

- Require both symbol+code in /setcurrency; add preset picker ($ USD,
  T Toman, IRR Rial, EUR, GBP) in settings inline menu
- League: compact 2-line per entry for mobile; sort buttons in 2x2 grid
- Settings: 2-column layout with grouped buttons (timezone+calendar,
  report+report time, break+accent, rpg+league, currency+rate)
- Burnout: cap break ratio at 100% to prevent nonsense values
- Add /setusername command (uses existing SanitizeDisplayName)
- Update /help with new/changed commands

internal/bot/handlers.go

@@ -215,6 +215,8 @@ func (h *Handler) HandleMessage(ctx context.Context, msg *models.Message) {
 		h.handleRPGSettingsMsg(ctx, msg)
 	case "/leaguetoggle":
 		h.handleLeagueSettingsMsg(ctx, msg)
+	case "/setusername":
+		h.handleSetUsername(ctx, msg)
 	default:
 		h.sendText(ctx, msg.Chat.ID, "Unknown command")
 	}
@@ -326,6 +328,10 @@ func (h *Handler) handlePrefixedCallback(ctx context.Context, chatID int64, msgI
 		h.selectBreakThreshold(ctx, chatID, msgID, callbackID, data[15:])
 		return
 	}
+	if len(data) > 9 && data[:9] == "currency_" {
+		h.selectCurrency(ctx, chatID, msgID, callbackID, data[9:])
+		return
+	}
 	switch data {
 	case "rpg_enable":
 		h.handleSelectCallback(ctx, chatID, msgID, callbackID, "rpg_enable", true)
@@ -399,13 +405,14 @@ func (h *Handler) handleHelp(ctx context.Context, msg *models.Message) {
 /setaccent - Select accent color
 /settimezone <name> - Set timezone (e.g. Asia/Tehran)
 /setbreak <minutes> - Set break threshold in minutes
+/setusername <name> - Set your display name
 /rpg - Show RPG stats and XP
 /achievements - View unlocked achievements
 /salary - Show salary estimate
 /burnout - View burnout assessment
 /league - View WorkTime League rankings
 /setrate <amount> - Set hourly rate (e.g. 25.50)
-/setcurrency <symbol> [code] - Set currency (e.g. $ USD)
+/setcurrency <symbol> <code> - Set currency (e.g. $ USD)
 /rpgtoggle - Enable/disable RPG system
 /leaguetoggle - Enable/disable league participation
 
@@ -414,6 +421,36 @@ Buttons on the main menu also work.`
 	h.sendText(ctx, msg.Chat.ID, text)
 }
 
+// handleSetUsername handles /setusername <name>.
+func (h *Handler) handleSetUsername(ctx context.Context, msg *models.Message) {
+	name := strings.TrimSpace(strings.TrimPrefix(msg.Text, "/setusername"))
+	if name == "" {
+		user, err := h.getOrCreateUser(msg.Chat.ID)
+		if err != nil {
+			h.sendText(ctx, msg.Chat.ID, "Error loading profile")
+			return
+		}
+		h.sendText(ctx, msg.Chat.ID, fmt.Sprintf("Current username: %s\nUsage: /setusername <name>", user.Username))
+		return
+	}
+	name = SanitizeDisplayName(name)
+	if name == "" {
+		h.sendText(ctx, msg.Chat.ID, "Invalid username.")
+		return
+	}
+	user, err := h.getOrCreateUser(msg.Chat.ID)
+	if err != nil {
+		h.sendText(ctx, msg.Chat.ID, "Error loading profile")
+		return
+	}
+	user.Username = name
+	if err := h.DB.UpdateUser(user); err != nil {
+		h.sendText(ctx, msg.Chat.ID, "Error saving username")
+		return
+	}
+	h.sendText(ctx, msg.Chat.ID, fmt.Sprintf("Username set to: %s", name))
+}
+
 // handleNoteMsg processes the /note command: /note [YYYY-MM-DD] HH:MM <text>
 func (h *Handler) handleNoteMsg(ctx context.Context, msg *models.Message) {
 	user, err := h.getOrCreateUser(msg.Chat.ID)