refactor: move backend files to backend/ directory

Reorganize project structure:
- backend/cmd/openteam/ — entry point
- backend/internal/ — core packages
- backend/middleware/ — HTTP middleware
- backend/router/ — route setup
- backend/wire/ — dependency injection
- backend/pkg/ — shared utilities
- backend/go.mod, go.sum — Go module files

Updated Makefile to work from backend/ directory.
Removed old lowercase makefile.

backend/internal/controller/proxy/proxy.go

@@ -0,0 +1,124 @@
+package proxy
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/url"
+	"opencatd-open/internal/channel"
+	"opencatd-open/internal/dao"
+	"opencatd-open/internal/store"
+	"opencatd-open/pkg/config"
+	"os"
+	"strings"
+	"sync"
+
+	"github.com/gin-gonic/gin"
+	"gorm.io/gorm"
+)
+
+type Proxy struct {
+	ctx        context.Context
+	cfg        *config.Config
+	db         *gorm.DB
+	wg         *sync.WaitGroup
+	httpClient *http.Client
+
+	userDAO    *dao.UserDAO
+	apiKeyDAO  *dao.ApiKeyDAO
+	usageDAO   *dao.UsageDAO
+	dailyDAO   *dao.DailyUsageDAO
+	channelSvc *channel.Service
+}
+
+func NewProxy(ctx context.Context, cfg *config.Config, db *gorm.DB, wg *sync.WaitGroup, userDAO *dao.UserDAO, apiKeyDAO *dao.ApiKeyDAO, usageDAO *dao.UsageDAO, dailyDAO *dao.DailyUsageDAO) *Proxy {
+	client := http.DefaultClient
+	if os.Getenv("LOCAL_PROXY") != "" {
+		proxyUrl, err := url.Parse(os.Getenv("LOCAL_PROXY"))
+		if err == nil {
+			tr := &http.Transport{
+				Proxy: http.ProxyURL(proxyUrl),
+			}
+			client.Transport = tr
+		}
+	}
+
+	np := &Proxy{
+		ctx:        ctx,
+		cfg:        cfg,
+		db:         db,
+		wg:         wg,
+		httpClient: client,
+		userDAO:    userDAO,
+		apiKeyDAO:  apiKeyDAO,
+		usageDAO:   usageDAO,
+		dailyDAO:   dailyDAO,
+	}
+
+	return np
+}
+
+// SetChannelService sets the channel service (called after construction)
+func (p *Proxy) SetChannelService(svc *channel.Service) {
+	p.channelSvc = svc
+}
+
+func (p *Proxy) HandleProxy(c *gin.Context) {
+	path := c.Request.URL.Path
+	switch {
+	case path == "/v1/chat/completions":
+		// TODO: Phase 3 - implement chat completions handler
+		c.JSON(http.StatusNotImplemented, gin.H{"error": "chat completions not yet implemented"})
+	case strings.HasPrefix(path, "/v1/messages"):
+		// TODO: Phase 3 - implement messages handler
+		c.JSON(http.StatusNotImplemented, gin.H{"error": "messages not yet implemented"})
+	case path == "/v1/responses":
+		// TODO: Phase 3 - implement responses handler
+		c.JSON(http.StatusNotImplemented, gin.H{"error": "responses not yet implemented"})
+	default:
+		c.JSON(http.StatusNotFound, gin.H{"error": "unknown endpoint"})
+	}
+}
+
+func (p *Proxy) HandleModels(c *gin.Context) {
+	// TODO: Phase 3 - implement models list
+	c.JSON(http.StatusOK, gin.H{"object": "list", "data": []interface{}{}})
+}
+
+func (p *Proxy) GetDB() *gorm.DB {
+	return p.db
+}
+
+// SelectChannel selects the best channel for a model
+func (p *Proxy) SelectChannel(modelName string) (*store.Channel, error) {
+	if p.channelSvc == nil {
+		return nil, fmt.Errorf("channel service not initialized")
+	}
+	return p.channelSvc.SelectChannel(p.ctx, modelName)
+}
+
+// RecordSuccess records a successful request
+func (p *Proxy) RecordSuccess(channelID uint64) {
+	if p.channelSvc != nil {
+		p.channelSvc.RecordSuccess(channelID)
+	}
+}
+
+// RecordFailure records a failed request
+func (p *Proxy) RecordFailure(channelID uint64) {
+	if p.channelSvc != nil {
+		p.channelSvc.RecordFailure(channelID)
+	}
+}
+
+// SendUsagePlaceholder placeholder for usage processing
+func (p *Proxy) SendUsagePlaceholder(model string, userID uint64, promptTokens, completionTokens int) {
+	log.Printf("Usage: model=%s user=%d prompt=%d completion=%d", model, userID, promptTokens, completionTokens)
+}
+
+// Placeholder to keep the file compilable
+var _ = json.Marshal
+var _ = io.ReadAll