feat(server): initialize project skeleton with db and api setup

Establish the foundational structure for the ez-api server.

Key changes include:
- Set up main entry point with graceful shutdown and Gin router
- Configure database connections for PostgreSQL (GORM) and Redis
- Define core data models (User, Provider, Key, Model)
- Implement configuration loading and basic key creation handler
- Add Dockerfile for multi-stage builds and .gitignore

internal/model/models.go

@@ -0,0 +1,37 @@
+package model
+
+import (
+	"gorm.io/gorm"
+)
+
+type User struct {
+	gorm.Model
+	Username string `gorm:"uniqueIndex;not null"`
+	Quota    int64  `gorm:"default:0"`
+	Role     string `gorm:"default:'user'"` // admin, user
+}
+
+type Provider struct {
+	gorm.Model
+	Name    string `gorm:"not null"`
+	Type    string `gorm:"not null"` // openai, anthropic, etc.
+	BaseURL string
+	APIKey  string
+}
+
+type Key struct {
+	gorm.Model
+	ProviderID *uint
+	Provider   *Provider
+	KeySecret  string `gorm:"not null"`
+	Balance    float64
+	Status     string `gorm:"default:'active'"` // active, suspended
+	Weight     int    `gorm:"default:10"`
+}
+
+type Model struct {
+	gorm.Model
+	Name          string `gorm:"uniqueIndex;not null"`
+	ContextWindow int
+	CostPerToken  float64
+}