i18n(es-419): complete Latin American Spanish translations (#2190)

* i18n(es-419): complete Latin American Spanish translations

Fill in all 737 previously untranslated strings in the es-419 admin
catalog, taking coverage from 61% to 100%. Terminology and voice follow
the existing catalog's conventions: formal usted for instructions,
infinitive for buttons and labels, "No se pudo X" for failure toasts,
and the settled es-419 terms (Agregar, respaldo, firma, entrada,
elemento). ICU plural structure, placeholders, tags, and significant
whitespace are preserved byte-exactly; the catalog compiles cleanly and
was previewed screen-by-screen in the running admin.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VYCQX2PNX4wir7DJctR2mn

* i18n(es-419): align "Job title" to "Cargo" across the byline feature

The field-label placeholder said "Puesto de trabajo" while the byline
schema help text modeled the same example as "Cargo".

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VYCQX2PNX4wir7DJctR2mn

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Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: edrpls

.changeset/es-419-complete-translations.md

@@ -0,0 +1,5 @@
+---
+"@emdash-cms/admin": patch
+---
+
+Completes the Latin American Spanish (es-419) admin UI translations — all 737 previously missing strings, covering the content editor, media library, settings and backups, WordPress import, bylines, widgets, taxonomies, users, and plugin screens.