Add inventory relations model and API structure

backend/app/routers/inventory.py

@@ -0,0 +1,48 @@
+from fastapi import APIRouter, HTTPException, Query
+
+from app.schemas import EntityResponse, InventoryTreeNode, ListResponse, NodeContext, Relation
+from app.services.inventory import build_inventory_tree, build_node_context, get_badges, get_node_relations
+
+router = APIRouter(prefix='/inventory', tags=['inventory'])
+
+
+@router.get('/tree', response_model=ListResponse[InventoryTreeNode])
+def inventory_tree(
+    root_id: str | None = None,
+    depth: int | None = Query(default=None, ge=0),
+) -> ListResponse[InventoryTreeNode]:
+    items = build_inventory_tree(root_id=root_id, depth=depth)
+    return ListResponse(count=len(items), items=items)
+
+
+@router.get('/tree/{item_id}', response_model=EntityResponse[InventoryTreeNode])
+def inventory_subtree(item_id: str, depth: int | None = Query(default=None, ge=0)) -> EntityResponse[InventoryTreeNode]:
+    items = build_inventory_tree(root_id=item_id, depth=depth)
+    if not items:
+        raise HTTPException(status_code=404, detail='Inventory node not found')
+    return EntityResponse(item=items[0])
+
+
+@router.get('/nodes/{item_id}/context', response_model=EntityResponse[NodeContext])
+def node_context(item_id: str) -> EntityResponse[NodeContext]:
+    item = build_node_context(item_id)
+    if not item:
+        raise HTTPException(status_code=404, detail='Inventory node not found')
+    return EntityResponse(item=item)
+
+
+@router.get('/nodes/{item_id}/badges', response_model=ListResponse[str])
+def node_badges(item_id: str) -> ListResponse[str]:
+    badges = get_badges(item_id)
+    return ListResponse(count=len(badges), items=badges)
+
+
+@router.get('/nodes/{item_id}/relations', response_model=ListResponse[Relation])
+def node_relations(
+    item_id: str,
+    layer: str | None = None,
+    type: str | None = Query(default=None),
+    direction: str = Query(default='both', pattern='^(incoming|outgoing|both)$'),
+) -> ListResponse[Relation]:
+    items = get_node_relations(item_id, layer=layer, rel_type=type, direction=direction)
+    return ListResponse(count=len(items), items=items)