Low-stock alerts for consumables (filter + API + dashboard helper)

Added a per-tool minStockLevel field (null = use org fallback of 5) and a lowStock=true filter on GET /api/v1/tools that returns consumables where stockLevel <= COALESCE(minStockLevel, 5). The /tools page picked up a 'Low stock' chip alongside All / Mine / Needs repair; rows now render the stock level inline with amber emphasis when low. A lowStockTools(orgId, limit) helper sorts asc by stockLevel for dashboard widgets. 17 new tests for isLowStock + lowStockTools + the API filter; 862 total pass.