refactor(B1): migrate to domain-driven project structure

Move all models/schemas/services/routers into app/domains/.
Keep backward-compat shims in old locations for imports.
Preserves domains/rendering/tasks.py from Phase A.

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

backend/app/domains/imports/__init__.py

@@ -0,0 +1 @@
+# Domain: imports

backend/app/domains/imports/models.py

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+import uuid
+from datetime import datetime
+from sqlalchemy import String, Boolean, DateTime, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from app.database import Base
+
+
+class Template(Base):
+    __tablename__ = "templates"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    category_key: Mapped[str] = mapped_column(String(100), unique=True, nullable=False, index=True)
+    # JSONB config for each of the 11 standard columns: {col_index: {label, required, optional}}
+    standard_fields: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict)
+    # JSONB schema for expected component pairs
+    component_schema: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict)
+    description: Mapped[str] = mapped_column(Text, nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+
+    orders: Mapped[list["Order"]] = relationship("Order", back_populates="template")

backend/app/domains/imports/router.py

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+# Re-export from original routers.
+from app.api.routers.uploads import router as uploads_router
+from app.api.routers.templates import router as templates_router
+
+__all__ = ["uploads_router", "templates_router"]

backend/app/domains/imports/schemas.py

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+from pydantic import BaseModel
+from typing import Any
+
+
+class ParsedComponent(BaseModel):
+    part_name: str | None = None
+    material: str | None = None
+    component_type: str | None = None
+    column_index: int
+
+
+class ParsedRow(BaseModel):
+    row_index: int
+    ebene1: str | None = None
+    ebene2: str | None = None
+    baureihe: str | None = None
+    pim_id: str | None = None
+    produkt_baureihe: str | None = None
+    gewaehltes_produkt: str | None = None
+    name_cad_modell: str | None = None
+    gewuenschte_bildnummer: str | None = None
+    lagertyp: str | None = None
+    medias_rendering: bool | None = None
+    components: list[ParsedComponent] = []
+
+
+class ParsedExcelResponse(BaseModel):
+    filename: str
+    excel_path: str | None = None   # server-side path of the saved file
+    category_key: str | None = None
+    template_name: str | None = None
+    row_count: int
+    column_headers: list[str]
+    rows: list[ParsedRow]
+    warnings: list[str] = []
+
+
+class StepUploadResponse(BaseModel):
+    cad_file_id: str
+    original_name: str
+    file_hash: str
+    status: str
+    matched_items: list[str] = []

backend/app/domains/imports/service.py

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+"""Import services — Excel parsing and product import."""
+
+# Re-export from original service files for backward compatibility.
+from app.services.excel_parser import parse_excel, parsed_excel_to_dict
+from app.services.excel_import import import_excel_to_products, preview_excel_rows
+
+__all__ = [
+    "parse_excel",
+    "parsed_excel_to_dict",
+    "import_excel_to_products",
+    "preview_excel_rows",
+]