Add habit statistics feature

- Implement GetHabitStatsHandler with streak calculations
- Calculate current streak, longest streak, and completion rate
- Track completions this week and this month
- Add stats HTTP handler and route at /api/v1/stats/habits/{id}
- Add Swagger documentation for stats endpoint

internal/infrastructure/http/router.go

@@ -13,7 +13,7 @@ import (
 	_ "apocapoc-api/docs"
 )
 
-func NewRouter(corsOrigins string, habitHandlers *HabitHandlers, authHandlers *AuthHandlers, jwtService *auth.JWTService) *chi.Mux {
+func NewRouter(corsOrigins string, habitHandlers *HabitHandlers, authHandlers *AuthHandlers, statsHandlers *StatsHandlers, jwtService *auth.JWTService) *chi.Mux {
 	r := chi.NewRouter()
 
 	r.Use(middleware.Logger)
@@ -55,5 +55,10 @@ func NewRouter(corsOrigins string, habitHandlers *HabitHandlers, authHandlers *A
 		r.Delete("/{id}/entries/{date}", habitHandlers.UnmarkHabit)
 	})
 
+	r.Route("/api/v1/stats", func(r chi.Router) {
+		r.Use(AuthMiddleware(jwtService))
+		r.Get("/habits/{id}", statsHandlers.GetHabitStats)
+	})
+
 	return r
 }