feat: add admin API endpoints for inventory transaction history

Adds admin endpoints for viewing transaction history across all vendors:
- GET /admin/inventory/transactions - paginated cross-vendor list
- GET /admin/inventory/transactions/stats - platform-wide statistics

Includes vendor details in transaction items and transaction counts
by type for dashboard displays.

🤖 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

@@ -22,6 +22,7 @@ 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 app.services.inventory_transaction_service import inventory_transaction_service
 from models.database.user import User
 from models.schema.inventory import (
     AdminInventoryAdjust,
@@ -29,7 +30,10 @@ from models.schema.inventory import (
     AdminInventoryListResponse,
     AdminInventoryLocationsResponse,
     AdminInventoryStats,
+    AdminInventoryTransactionItem,
+    AdminInventoryTransactionListResponse,
     AdminLowStockItem,
+    AdminTransactionStatsResponse,
     AdminVendorsWithInventoryResponse,
     InventoryAdjust,
     InventoryCreate,
@@ -378,3 +382,52 @@ async def import_inventory(
         unmatched_gtins=[UnmatchedGtin(**g) for g in result.unmatched_gtins],
         errors=result.errors,
     )
+
+
+# ============================================================================
+# Transaction History Endpoints
+# ============================================================================
+
+
+@router.get("/transactions", response_model=AdminInventoryTransactionListResponse)
+def get_all_transactions(
+    skip: int = Query(0, ge=0),
+    limit: int = Query(50, ge=1, le=200),
+    vendor_id: int | None = Query(None, description="Filter by vendor"),
+    product_id: int | None = Query(None, description="Filter by product"),
+    transaction_type: str | None = Query(None, description="Filter by type"),
+    order_id: int | None = Query(None, description="Filter by order"),
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """
+    Get inventory transaction history across all vendors.
+
+    Returns a paginated list of all stock movements with vendor and product details.
+    """
+    transactions, total = inventory_transaction_service.get_all_transactions_admin(
+        db=db,
+        skip=skip,
+        limit=limit,
+        vendor_id=vendor_id,
+        product_id=product_id,
+        transaction_type=transaction_type,
+        order_id=order_id,
+    )
+
+    return AdminInventoryTransactionListResponse(
+        transactions=[AdminInventoryTransactionItem(**tx) for tx in transactions],
+        total=total,
+        skip=skip,
+        limit=limit,
+    )
+
+
+@router.get("/transactions/stats", response_model=AdminTransactionStatsResponse)
+def get_transaction_stats(
+    db: Session = Depends(get_db),
+    current_admin: User = Depends(get_current_admin_api),
+):
+    """Get transaction statistics for the platform."""
+    stats = inventory_transaction_service.get_transaction_stats_admin(db)
+    return AdminTransactionStatsResponse(**stats)