Add complete database schema and ORM models (#4)

internal/models/server_link.go

@@ -0,0 +1,18 @@
+package models
+
+import (
+	"time"
+)
+
+// ServerLink represents a federation peer server configuration.
+type ServerLink struct {
+	Base
+
+	ID            string     `json:"id"`
+	Name          string     `json:"name"`
+	URL           string     `json:"url"`
+	SharedKeyHash string     `json:"-"`
+	IsActive      bool       `json:"isActive"`
+	CreatedAt     time.Time  `json:"createdAt"`
+	LastSeenAt    *time.Time `json:"lastSeenAt,omitempty"`
+}