feat: add finance module with yearly income/expense tracking

- FinanceEntry model (income/expense x fixed/extra)
- CRUD API endpoints for finance entries
- FinancePage with summary cards and drill-down
- Updated navigation with Finance tab
- Updated todos default filter to active

internal/model/model.go

@@ -31,3 +31,22 @@ type DailyLog struct {
 func (DailyLog) TableName() string {
 	return "daily_logs"
 }
+
+// FinanceEntry 收支条目
+// Type: income(收入) / expense(支出)
+// Category: fixed(固定) / extra(额外)
+type FinanceEntry struct {
+	ID          uint64    `gorm:"primaryKey;autoIncrement" json:"id"`
+	Year        int       `gorm:"type:int;not null;index" json:"year"`                     // 年份
+	Month       int       `gorm:"type:int;not null;default:0" json:"month"`                // 月份（0表示全年）
+	Type        string    `gorm:"type:varchar(10);not null" json:"type"`                  // income / expense
+	Category    string    `gorm:"type:varchar(10);not null" json:"category"`               // fixed / extra
+	Description string    `gorm:"type:varchar(255)" json:"description"`                   // 条目描述
+	Amount      float64   `gorm:"type:decimal(12,2);not null" json:"amount"`             // 金额（正数）
+	CreatedAt   time.Time `gorm:"autoCreateTime" json:"created_at"`
+	UpdatedAt   time.Time `gorm:"autoUpdateTime" json:"updated_at"`
+}
+
+func (FinanceEntry) TableName() string {
+	return "finance_entries"
+}