In Multiwebsite settings, when the public user interactions needs email generation (appointment or event flow), the email links are generated with a base url that does not corresponds to the one from which the request started.

Case 1:
- Have website A and website B
- Create an appointment page website A
- Log in via website B
- As public user, make an appointment in Website A
- Check the generated email

Issue: button links in the email will redirect to the wrong website, so users will encounter an issue when managing the appointment. This occurs because when an user log in, the system parameter 'web.base_url' is updated with the current url.
This parameter is then used as fallback when we need to retrieve the base url without an active record

Case 2:
- Have website A and website B
- Create an event and assign it to website B
- As public user, access the event and register to it
- Check the generated email

Issue: button links in the email will redirect to the wrong website, so users will encounter an issue when managing the event.
This occurs because the record `event.registration` has no website_id field and the base url is taken from the company default website (website A)

Backport with improvements of 15bae202d8f1b5bf70bbc63b2d89025e9237e6cf

opw-4146760
opw-4336369

Forward-Port-Of: odoo/enterprise#124173
Forward-Port-Of: odoo/enterprise#122669

## Context

When generating a CFE (Comprobante Fiscal Electrónico) that contains both a configured addenda (e.g. bank account details stored in `l10n_uy_edi_addenda_ids`) and terms & conditions from the invoice's `narration` field, the resulting addenda string could end up with unnecessary blank lines between the two sections, causing the addenda to be rendered on a separate page even when the logical content fits within the 6-line threshold.

## Root Cause

`_l10n_uy_edi_get_addenda` joins both parts without stripping whitespace from either of them first, and adds two lines between addendas and terms and conditions:

         addenda = addenda + "\n\n" + term_and_conditions if addenda else term_and_conditions

Two sources independently introduce extra newlines around the separator:

1. **Addenda content** — `_get_legends` returns the raw `content`  field value of each addenda record. These fields commonly end  with a trailing `\n`, so the addenda string already ends with a newline before the `"\n"` separator is concatenated.
2. **`html2plaintext`** — the `narration` field is stored as HTML. When converted to plain text, `html2plaintext` typically wraps paragraph content in leading/trailing newlines.

The combination of the trailing `\n` from the addenda, the explicit `"\n\n"` separator, and the leading/trailing `\n` from `html2plaintext` produces 2–3 consecutive newlines, which `splitlines()` counts as blank lines. 
A realistic 4-line addenda + 1-line narration thus produces **7 lines** instead of the expected 5, crossing the 6-line threshold in `_get_report_params` and triggering `adenda=true` — which forces the addenda onto a separate page unnecessarily.

## Steps to Reproduce

1. Configure a `l10n_uy_edi.addenda` record of type `addenda` with multi-line content (4 lines)
2. Create and confirm an invoice with `narration` set to a short  single-line term 
3. Generate the CFE PDF via Uruware.
4. Observe that the addenda is rendered on a separate page despite the logical content being only 5 lines.

<img width="1042" height="448" alt="image" src="https://github.com/user-attachments/assets/b538211c-5f37-4648-979d-99cd75cf31c2" />


## Fix

Strip leading and trailing whitespace (including newlines) from both parts before joining them. The ternary is also replaced with an explicit `if/else` for clarity:

    def _l10n_uy_edi_get_addenda(self):
        addenda = self.l10n_uy_edi_document_id._get_legends("addenda", self)
        if self.narration:
            term_and_conditions = html2plaintext(self.narration).strip()
            if addenda:
                addenda = addenda.strip() + "\n" + term_and_conditions
            else:
                addenda = term_and_conditions
        return self._l10n_uy_edi_clean_non_ascii_chars(addenda)

This guarantees exactly one `\n` separator between sections regardless of how the content fields were stored or how `html2plaintext` formatted the narration.

The threshold logic in `_get_report_params` is unchanged: addendas that genuinely exceed 6 lines (after wrapping at 140 chars) continue to be printed on a dedicated page.

Result
<img width="1117" height="456" alt="image" src="https://github.com/user-attachments/assets/3a2d942c-8c37-40f6-bc25-470c0bd25b08" />

Forward-Port-Of: odoo/enterprise#119283