## 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