* feat(eu_einvoice): configurable base name for auto-attached XRechnung XML

Add optional pattern on E Invoice Settings (auto_name_format_for_xml_file) for the
file base name when auto-attaching XML on Sales Invoice submit. Empty pattern keeps
using the document name; otherwise use naming-series-style segments (dot-separated,
parse_naming_series, {field} placeholders, date tokens), strip leading # per
segment so counter-only parts do not consume Series, sanitize with get_safe_file_name,
and fall back to the document name on error.

Colocate get_xml_attachment_file_base_name with Sales Invoice custom logic and cover
naming edge cases in test_sales_invoice.py.

Refresh E Invoice Settings controller and de / template catalogs for the new strings.

* refactor(eu_einvoice): enhance download_xrechnung to use configurable base name

Update the download_xrechnung function to retrieve the Sales Invoice document
and check permissions before generating the XML file.
The filename now utilizes a configurable base name from E Invoice Settings,
improving flexibility for file naming.
This change ensures that the generated XML file adheres to the specified naming format.

* chore(eu_einvoice): update E Invoice Settings and localization files

Rearrange fields in e_invoice_settings.json for better organization, adding a label for
the XML Settings section. Update localization files (de.po and main.pot) to reflect
changes in field names and add new translations for XML Settings.
Adjust POT creation dates for consistency.

* refactor(eu_einvoice): centralize sales invoice xml stem naming

Resolve the downloadable XML filename stem in get_xml_attachment_file_base_name:
read *Auto name format for XML file* from **E Invoice Settings** when the pattern
argument is omitted, accept an optional keyword-only pattern override, and build
the stem with parse_naming_series plus a no-op number generator so naming has no
series counter DB side effects. Sanitize with get_safe_file_name and fall back to
doc.name when the pattern is empty or fails.

Call sites use the helper without duplicating settings reads. Tests pass pattern=
for empty or whitespace patterns, and assert the settings-backed path by patching
frappe.get_single_value only for **E Invoice Settings** / auto_name_format_for_xml_file.

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Co-authored-by: Daniel Rose <26166128+dafrose@users.noreply.github.com>
(cherry picked from commit d45a1f0)
Co-authored-by: Cursor <cursoragent@cursor.com>