Issue:
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There is a fiscal regime where the company is actually an individual but is authorized to generate documents.

Steps to reproduce:
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- Install "l10n_mx_hr_payroll_account_edi"
- Change the current company fiscal regime to '621'
- Add an VAT of length 13 to the current company
- Add a CURP number on the current company
- In Payroll generate a payslip, validate it
- Post the Journal entry
- On the payslip, click "Generate CFDI"
- An error is returned, saying the Emisor:Curp applies to individuals

Cause:
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An RFC of length 13 means that the sender is an individual. It's intended with the fiscal regime '621'.

We add the curp number in the CFDI XML only when `self.company_id.partner_id.is_company` is `False`. Since saas-19.1, `is_company` is computed to be truely if a VAT is present. So as soon as the VAT is entered, the CURP number is absent from the XML.

Solution:
----------------------------------------
We change the condition to add the CURP number in the XML: A VAT number of length 13 means the contact is an individual (12 for companies). This is what is used to validate the XML: if the vat is of length 13, then the curp number should be present.

opw-6351558

Forward-Port-Of: odoo/enterprise#124728
Forward-Port-Of: odoo/enterprise#124027

Steps to reproduce:
- install Timesheets
- create an employee for a user in company B
- switch to company A (where the user has no employee)
- the systray icon is hidden even though the user can
create timesheets in company B via the company selector

Current behavior:
the systray only checks the current company for a valid
employee, ignoring other selected companies.

Expected behavior:
the systray should be visible whenever the user can create
timesheets i.e. when they have an active employee in any
of the selected companies.

Issue:
the check used a stored boolean on `res.partner` that has no
company scope and becomes stale when an employee is archived
(the stored dependency does not re-fire). the timesheet
creation logic checks all selected companies for active
employees, but the systray did not mirror that.

Fix:
use `employee_ids` a `One2many` that checks all selected
companies and excludes archived employees, matching the
timesheet creation logic exactly.

task-6330539

Forward-Port-Of: odoo/enterprise#124761
Forward-Port-Of: odoo/enterprise#121730