refactor: complete backend rewrite for multi-protocol proxy

Major rewrite of the Go backend to support:
- Three API format imports: openai, anthropic, compatible
- Three protocol conversions: Chat Completions, Responses, Messages
- Hub-and-spoke architecture with Chat as intermediate format

Deleted:
- opencat.go (old entry)
- store/, team/, pkg/team/, pkg/store/ (old data layer)
- internal/model/, internal/consts/ (old types)
- internal/service/team/, internal/controller/team/ (old handlers)
- llm/ (removed LLM client library, pure proxy mode)
- dist/, assets/ (old build artifacts)

Added:
- internal/store/ — 9 GORM models + multi-DB support
- internal/pkg/ — crypto (AES-GCM), apikey, jwt, ratelimit, resp, tokenizer
- internal/channel/ — channel selection, weighted LB, health checks
- internal/proxy/convert/ — 6 protocol conversion functions + SSE streaming
- internal/proxy/ — gateway with request dispatch and upstream selection
- internal/usage/ — async usage recorder with batch writes
- internal/api/ — management API (auth, users, keys, channels, models)
- Makefile for build/test/deploy

Fixed API to match frontend expectations:
- Login response wraps token in { data: { token } }
- GET /api/profile route added
- Profile response wraps user in { code, data }
- Role returned as number (10=admin, 1=user)

internal/dto/team/team.go

@@ -1,83 +0,0 @@
-package dto
-
-import (
-	"opencatd-open/internal/model"
-	"opencatd-open/internal/utils"
-)
-
-type UserInfo struct {
-	ID     int64  `json:"id"`
-	Name   string `json:"name"`
-	Token  string `json:"token"`
-	Status *bool  `json:"status,omitempty"`
-}
-
-func (u UserInfo) HasNameUpdate() bool {
-	return u.Name != ""
-}
-
-func (u UserInfo) HasTokenUpdate() bool {
-	return u.Token != ""
-}
-
-func (u UserInfo) HasStatusUpdate() bool {
-	return u.Status != nil
-}
-
-type ApiKeyInfo struct {
-	ID       int    `json:"id,omitempty"`
-	Key      string `json:"key,omitempty"`
-	Name     string `json:"name,omitempty"`
-	ApiType  string `json:"api_type,omitempty"`
-	Endpoint string `json:"endpoint,omitempty"`
-	Status   *bool  `json:"status,omitempty"`
-}
-
-// 添加辅助方法判断字段是否需要更新
-func (k ApiKeyInfo) HasNameUpdate() bool {
-	return k.Name != ""
-}
-
-func (k ApiKeyInfo) HasKeyUpdate() bool {
-	return k.Key != ""
-}
-
-func (k ApiKeyInfo) HasStatusUpdate() bool {
-	return k.Status != nil
-}
-
-func (k ApiKeyInfo) HasApiTypeUpdate() bool {
-	return k.ApiType != ""
-}
-
-// 辅助函数：统一处理字段更新
-func (update *ApiKeyInfo) UpdateFields(existing *model.ApiKey) *model.ApiKey {
-	result := &model.ApiKey{
-		ID:      existing.ID,
-		Name:    existing.Name,    // 默认保持原值
-		ApiType: existing.ApiType, // 默认保持原值
-		ApiKey:  existing.ApiKey,  // 默认保持原值
-		Active:  existing.Active,  // 默认保持原值
-	}
-
-	if update.HasNameUpdate() {
-		result.Name = utils.ToPtr(update.Name)
-	}
-	if update.HasKeyUpdate() {
-		result.ApiKey = utils.ToPtr(update.Key)
-	}
-	if update.HasStatusUpdate() {
-		result.Active = update.Status
-	}
-	if update.HasApiTypeUpdate() {
-		result.ApiType = utils.ToPtr(update.ApiType)
-	}
-
-	return result
-}
-
-type UsageInfo struct {
-	UserId    int    `json:"userId"`
-	TotalUnit int    `json:"totalUnit"`
-	Cost      string `json:"cost"`
-}