refactor: restructure internal/ into adapters/, infra/, and app layers

- internal/gemini/ → internal/adapters/openai/ (renamed package to openai)
- internal/pexels/ → internal/adapters/pexels/
- internal/config/   → internal/infra/config/
- internal/database/ → internal/infra/database/
- internal/locale/   → internal/infra/locale/
- internal/middleware/ → internal/infra/middleware/
- internal/server/   → internal/infra/server/

All import paths and call sites updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/cmd/server/providers.go

@@ -5,22 +5,22 @@ import (
 	"time"
 
 	"github.com/food-ai/backend/internal/auth"
-	"github.com/food-ai/backend/internal/config"
+	"github.com/food-ai/backend/internal/infra/config"
 	"github.com/food-ai/backend/internal/diary"
 	"github.com/food-ai/backend/internal/dish"
-	"github.com/food-ai/backend/internal/gemini"
+	"github.com/food-ai/backend/internal/adapters/openai"
 	"github.com/food-ai/backend/internal/home"
 	"github.com/food-ai/backend/internal/ingredient"
 	"github.com/food-ai/backend/internal/menu"
-	"github.com/food-ai/backend/internal/middleware"
-	"github.com/food-ai/backend/internal/pexels"
+	"github.com/food-ai/backend/internal/infra/middleware"
+	"github.com/food-ai/backend/internal/adapters/pexels"
 	"github.com/food-ai/backend/internal/product"
 	"github.com/food-ai/backend/internal/recipe"
 	"github.com/food-ai/backend/internal/recognition"
 	"github.com/food-ai/backend/internal/recommendation"
 	"github.com/food-ai/backend/internal/savedrecipe"
 	"github.com/food-ai/backend/internal/cuisine"
-	"github.com/food-ai/backend/internal/server"
+	"github.com/food-ai/backend/internal/infra/server"
 	"github.com/food-ai/backend/internal/tag"
 	"github.com/food-ai/backend/internal/units"
 	"github.com/food-ai/backend/internal/user"
@@ -38,7 +38,7 @@ type tagListHandler     http.HandlerFunc
 
 // ---------------------------------------------------------------------------
 
-type geminiAPIKey       string
+type openaiAPIKey       string
 type pexelsAPIKey       string
 type jwtSecret          string
 type jwtAccessDuration  time.Duration
@@ -49,8 +49,8 @@ type allowedOrigins     []string
 // Config extractors
 // ---------------------------------------------------------------------------
 
-func newGeminiAPIKey(appConfig *config.Config) geminiAPIKey {
-	return geminiAPIKey(appConfig.OpenAIAPIKey)
+func newOpenAIAPIKey(appConfig *config.Config) openaiAPIKey {
+	return openaiAPIKey(appConfig.OpenAIAPIKey)
 }
 
 func newPexelsAPIKey(appConfig *config.Config) pexelsAPIKey {
@@ -83,8 +83,8 @@ func newFirebaseCredentialsFile(appConfig *config.Config) string {
 // Constructor wrappers for functions that accept primitive newtypes
 // ---------------------------------------------------------------------------
 
-func newGeminiClient(key geminiAPIKey) *gemini.Client {
-	return gemini.NewClient(string(key))
+func newOpenAIClient(key openaiAPIKey) *openai.Client {
+	return openai.NewClient(string(key))
 }
 
 func newPexelsClient(key pexelsAPIKey) *pexels.Client {