docs: add Spanish (es) translation agent skill and locale guidelines (#63405)

Adds locales/es.md following the structure of the merged French skill
(#62161), with fixes based on review feedback from #62155.

Key decisions and rationale:
- Section 1 split into two lists: global Airflow terms that are never
  translated across all locales (Airflow, Dag, XCom, Schema, etc.) and
  a separate "Kept in English by convention (Spanish-specific)" list of
  terms the existing Spanish locale files leave untranslated (Backfill,
  Pool, Executor, Heartbeat, Upstream/Downstream, etc.). The distinction
  matters because the second list reflects established Spanish translations
  and could differ in other locales.
- Trigger/Triggerer handled as mixed usage: as a verb → "Activar"
  ("Activado por" for "Triggered by"); as a noun/component label →
  keep in English ("Clase del Trigger", "Triggerer Asignado"). Section 1,
  the standard translations table, and the examples block all
  cross-reference each other to prevent agents from defaulting to
  "disparador".
- Audit Log preferred as "Auditoría de Log" (correct noun form) over
  "Auditar Log" found in common.json; inconsistency flagged in the table.
- Filter split into noun ("Filtro") and verb ("Filtrar") — both forms
  appear in the existing translations.
- Spanish uses i18next suffixes _one and _other only; _many must always
  match _other.
- Hotkey literal values (e.g. "e") must not be translated.
- "Cannot X" dialog titles require a full phrase: "No Se Puede Limpiar
  la Instancia de Tarea" — do not shorten at the expense of meaning.
- Lines are not artificially wrapped; editors handle wrapping. This
  matches the style of the file rather than imposing an arbitrary
  column limit.

Co-authored-by: slegarraga <slegarraga@users.noreply.github.com>