feat(savings): Add savings module with categories, transactions, recurring plans

- Categories: regular, deposits, credits, recurring, multi-user, accounts
- Transactions: deposits and withdrawals with user tracking
- Recurring plans: monthly payment obligations per user
- Stats: overdues calculation with allocation algorithm
- Excludes is_account categories from total sums
- Documentation: docs/SAVINGS.md

internal/model/habit_freeze.go

@@ -0,0 +1,21 @@
+package model
+
+import (
+	"time"
+)
+
+type HabitFreeze struct {
+	ID        int64     `db:"id" json:"id"`
+	HabitID   int64     `db:"habit_id" json:"habit_id"`
+	UserID    int64     `db:"user_id" json:"user_id"`
+	StartDate time.Time `db:"start_date" json:"start_date"`
+	EndDate   time.Time `db:"end_date" json:"end_date"`
+	Reason    string    `db:"reason" json:"reason"`
+	CreatedAt time.Time `db:"created_at" json:"created_at"`
+}
+
+type CreateHabitFreezeRequest struct {
+	StartDate string `json:"start_date"`
+	EndDate   string `json:"end_date"`
+	Reason    string `json:"reason,omitempty"`
+}