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/stats_handlers.go

@@ -0,0 +1,66 @@
+package http
+
+import (
+	"net/http"
+
+	"apocapoc-api/internal/application/queries"
+	"apocapoc-api/internal/shared/errors"
+
+	"github.com/go-chi/chi/v5"
+)
+
+type StatsHandlers struct {
+	getHabitStatsHandler *queries.GetHabitStatsHandler
+}
+
+func NewStatsHandlers(
+	getHabitStatsHandler *queries.GetHabitStatsHandler,
+) *StatsHandlers {
+	return &StatsHandlers{
+		getHabitStatsHandler: getHabitStatsHandler,
+	}
+}
+
+// GetHabitStats godoc
+// @Summary Get habit statistics
+// @Description Get statistics for a specific habit including streaks and completion rates
+// @Tags stats
+// @Produce json
+// @Security BearerAuth
+// @Param id path string true "Habit ID"
+// @Success 200 {object} queries.HabitStatsDTO
+// @Failure 401 {object} ErrorResponse
+// @Failure 403 {object} ErrorResponse
+// @Failure 404 {object} ErrorResponse
+// @Failure 500 {object} ErrorResponse
+// @Router /stats/habits/{id} [get]
+func (h *StatsHandlers) GetHabitStats(w http.ResponseWriter, r *http.Request) {
+	habitID := chi.URLParam(r, "id")
+
+	userID, ok := GetUserIDFromContext(r.Context())
+	if !ok {
+		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		return
+	}
+
+	query := queries.GetHabitStatsQuery{
+		HabitID: habitID,
+		UserID:  userID,
+	}
+
+	stats, err := h.getHabitStatsHandler.Handle(r.Context(), query)
+	if err != nil {
+		if err == errors.ErrNotFound {
+			respondError(w, http.StatusNotFound, "Habit not found")
+			return
+		}
+		if err == errors.ErrUnauthorized {
+			respondError(w, http.StatusForbidden, "Access denied")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "Failed to get habit stats")
+		return
+	}
+
+	respondJSON(w, http.StatusOK, stats)
+}