refactor(phase3-session-b4): remove legacy router, __init__.py creates router directly

- Deleted empty routers/image_studio_router.py (legacy file)
- __init__.py now creates APIRouter directly instead of re-exporting from legacy
- Same prefix, tags, and all 33 routes preserved
- app.py imports unchanged: from routers.image_studio import router as image_studio_router

Final package structure:
routers/image_studio/
  ├── __init__.py  ← creates router, includes 10 sub-routers
  ├── models.py    ← 40 Pydantic models
  ├── deps.py      ← shared dependencies
  ├── create.py edit.py face_swap.py upscale.py  ← endpoint groups
  ├── control.py social.py transform.py
  ├── compress.py convert.py health.py

backend/routers/image_studio/__init__.py

@@ -1,10 +1,10 @@
 """Image Studio API router package.
 
 Composed from modular sub-routers. Same prefix and tags as the original monolithic file.
-Legacy router is kept as an empty anchor for backward compatibility.
 """
 
-from ..image_studio_router import router as legacy_router
+from fastapi import APIRouter
+
 from .health import router as health_router
 from .upscale import router as upscale_router
 from .control import router as control_router
@@ -16,17 +16,17 @@ from .transform import router as transform_router
 from .compress import router as compress_router
 from .convert import router as convert_router
 
-legacy_router.include_router(health_router)
-legacy_router.include_router(upscale_router)
-legacy_router.include_router(control_router)
-legacy_router.include_router(social_router)
-legacy_router.include_router(edit_router)
-legacy_router.include_router(face_swap_router)
-legacy_router.include_router(create_router)
-legacy_router.include_router(transform_router)
-legacy_router.include_router(compress_router)
-legacy_router.include_router(convert_router)
+router = APIRouter(prefix="/api/image-studio", tags=["image-studio"])
 
-router = legacy_router
+router.include_router(health_router)
+router.include_router(upscale_router)
+router.include_router(control_router)
+router.include_router(social_router)
+router.include_router(edit_router)
+router.include_router(face_swap_router)
+router.include_router(create_router)
+router.include_router(transform_router)
+router.include_router(compress_router)
+router.include_router(convert_router)
 
 __all__ = ["router"]

backend/routers/image_studio_router.py

@@ -1,48 +0,0 @@
-"""API endpoints for Image Studio operations."""
-
-import base64
-from pathlib import Path
-from typing import Dict, Any, Optional
-from fastapi import APIRouter, Depends, HTTPException, status, Query
-from fastapi.responses import FileResponse
-
-from .image_studio.models import (
-    CreateImageRequest, CostEstimationRequest,
-    EditImageRequest, EditImageResponse, EditOperationsResponse,
-    EditModelsResponse, EditModelRecommendationRequest, EditModelRecommendationResponse,
-    UpscaleImageRequest, UpscaleImageResponse,
-    FaceSwapRequest, FaceSwapResponse, FaceSwapModelsResponse,
-    FaceSwapModelRecommendationRequest, FaceSwapModelRecommendationResponse,
-    ControlImageRequest, ControlImageResponse, ControlOperationsResponse,
-    SocialOptimizeRequest, SocialOptimizeResponse, PlatformFormatsResponse,
-    TransformImageToVideoRequestModel, TalkingAvatarRequestModel,
-    TransformVideoResponse, TransformCostEstimateRequest, TransformCostEstimateResponse,
-    CompressImageRequest, CompressImageResponse, CompressBatchRequest, CompressBatchResponse,
-    CompressionEstimateRequest, CompressionEstimateResponse,
-    CompressionFormatsResponse, CompressionPresetsResponse,
-    ConvertFormatRequest, ConvertFormatResponse, ConvertFormatBatchRequest, ConvertFormatBatchResponse,
-    SupportedFormatsResponse, FormatRecommendationsResponse,
-)
-from .image_studio.deps import get_studio_manager, _require_user_id
-from services.image_studio import (
-    ImageStudioManager,
-    CreateStudioRequest,
-    EditStudioRequest,
-    ControlStudioRequest,
-    SocialOptimizerRequest,
-    TransformImageToVideoRequest,
-    TalkingAvatarRequest,
-)
-from services.image_studio.face_swap_service import FaceSwapStudioRequest
-from services.image_studio.upscale_service import UpscaleStudioRequest
-from services.image_studio.templates import Platform, TemplateCategory
-from middleware.auth_middleware import get_current_user, get_current_user_with_query_token
-from utils.logger_utils import get_service_logger
-
-
-logger = get_service_logger("api.image_studio")
-router = APIRouter(prefix="/api/image-studio", tags=["image-studio"])
-
-
-
-