[18.0][FEAT] Multi-company reports: companies as columns instead of extra rows

[dnplkndll]

Feature request

When multi_company=True on a MIS report instance, account detail rows currently show the company name as a suffix: 600000 Expenses [Branch Office]. Each company gets its own row.

It would be useful to have an option to show companies as columns instead — each company gets a column header, with the values side-by-side.

Current behavior (rows per company)

                    Year to Date
Expenses            $ 37,000
  600000 [Branch]   $ 22,000
  600000 [YourCo]   $ 15,000
Total               $ 37,000

Desired behavior (columns per company)

                    YourCompany    Branch Office    Total
Expenses            $ 15,000       $ 22,000        $ 37,000
  600000 Expenses   $ 15,000       $ 22,000        $ 37,000
Total               $ 15,000       $ 22,000        $ 37,000

Proposed implementation

Add an optional company_id field to mis.report.instance.period. When set, the period's query filters to that company only. Combined with comparison_mode=True, this creates one column per company.

A "Generate Company Columns" button on the instance form could auto-create one period per company in company_ids, each with the same date range but filtered to a different company.

Use case

Multi-company organizations that want to compare expenses, revenue, or KPIs across subsidiaries side-by-side in a single report, rather than scanning duplicate rows.