feat(stats): add command usage statistics module with persistence

Implement a new stats module for the Telegram bot that tracks per-command usage with persistent KV storage. The module provides a /stats command displaying usage sorted by popularity with a 4096-byte Telegram message cap. Includes CommandHook integration for post-dispatch tracking via background goroutine (2s bounded context), proper test coverage, and registry initialization. Updated server config with stats factory and reserved concurrent execution control to prevent TOCTOU issues.

cmd/server/main.go

@@ -23,6 +23,7 @@ import (
 	"github.com/tiennm99/miti99bot/internal/modules/loldle"
 	"github.com/tiennm99/miti99bot/internal/modules/lolschedule"
 	"github.com/tiennm99/miti99bot/internal/modules/misc"
+	"github.com/tiennm99/miti99bot/internal/modules/stats"
 	"github.com/tiennm99/miti99bot/internal/modules/trading"
 	"github.com/tiennm99/miti99bot/internal/modules/twentyq"
 	"github.com/tiennm99/miti99bot/internal/modules/util"
@@ -49,6 +50,7 @@ func factories() map[string]modules.Factory {
 		"lolschedule": lolschedule.New,
 		"twentyq":     twentyq.New,
 		"trading":     trading.New,
+		"stats":       stats.New,
 	}
 }