feat: add inventory CSV import with warehouse/bin locations

- Add warehouse and bin_location columns to Inventory model
- Create inventory_import_service for bulk TSV/CSV import
- Add POST /api/v1/admin/inventory/import endpoint
- Add Import button and modal to inventory admin page
- Support both single-unit rows and explicit QUANTITY column

File format: BIN, EAN, PRODUCT (optional), QUANTITY (optional)
Products matched by GTIN/EAN, unmatched items reported.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/admin/inventory.py

@@ -14,11 +14,13 @@ Vendor selection is passed as a request parameter.
 
 import logging
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, File, Form, Query, UploadFile
+from pydantic import BaseModel
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_admin_api
 from app.core.database import get_db
+from app.services.inventory_import_service import inventory_import_service
 from app.services.inventory_service import inventory_service
 from models.database.user import User
 from models.schema.inventory import (
@@ -284,3 +286,95 @@ def delete_inventory(
 
     db.commit()
     return InventoryMessageResponse(message="Inventory deleted successfully")
+
+
+# ============================================================================
+# Import Endpoints
+# ============================================================================
+
+
+class UnmatchedGtin(BaseModel):
+    """GTIN that couldn't be matched to a product."""
+
+    gtin: str
+    quantity: int
+    product_name: str
+
+
+class InventoryImportResponse(BaseModel):
+    """Response from inventory import."""
+
+    success: bool
+    total_rows: int
+    entries_created: int
+    entries_updated: int
+    quantity_imported: int
+    unmatched_gtins: list[UnmatchedGtin]
+    errors: list[str]
+
+
+@router.post("/import", response_model=InventoryImportResponse)
+async def import_inventory(
+    file: UploadFile = File(..., description="TSV/CSV file with BIN, EAN, PRODUCT, QUANTITY columns"),
+    vendor_id: int = Form(..., description="Vendor ID"),
+    warehouse: str = Form("strassen", description="Warehouse name"),
+    clear_existing: bool = Form(False, description="Clear existing inventory before import"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Import inventory from a TSV/CSV file.
+
+    File format (TSV recommended):
+    - Required columns: BIN, EAN
+    - Optional columns: PRODUCT (for display), QUANTITY (defaults to 1 per row)
+
+    If QUANTITY column is present, each row represents the quantity specified.
+    If QUANTITY is absent, each row counts as 1 unit (rows with same EAN+BIN are summed).
+
+    Products are matched by GTIN/EAN. Unmatched GTINs are reported in the response.
+    """
+    # Verify vendor exists
+    inventory_service.verify_vendor_exists(db, vendor_id)
+
+    # Read file content
+    content = await file.read()
+    try:
+        content_str = content.decode("utf-8")
+    except UnicodeDecodeError:
+        content_str = content.decode("latin-1")
+
+    # Detect delimiter
+    first_line = content_str.split("\n")[0] if content_str else ""
+    delimiter = "\t" if "\t" in first_line else ","
+
+    # Run import
+    result = inventory_import_service.import_from_text(
+        db=db,
+        content=content_str,
+        vendor_id=vendor_id,
+        warehouse=warehouse,
+        delimiter=delimiter,
+        clear_existing=clear_existing,
+    )
+
+    if result.success:
+        db.commit()
+        logger.info(
+            f"Admin {current_admin.email} imported inventory: "
+            f"{result.entries_created} created, {result.entries_updated} updated, "
+            f"{result.quantity_imported} total units"
+        )
+    else:
+        db.rollback()
+        logger.error(f"Inventory import failed: {result.errors}")
+
+    return InventoryImportResponse(
+        success=result.success,
+        total_rows=result.total_rows,
+        entries_created=result.entries_created,
+        entries_updated=result.entries_updated,
+        quantity_imported=result.quantity_imported,
+        unmatched_gtins=[UnmatchedGtin(**g) for g in result.unmatched_gtins],
+        errors=result.errors,
+    )