feat: i18n template infrastructure — render.sh reads _en vars, emits data-de/data-en
Phase 1 of i18n rollout:
- render.sh: i18n_attrs helper, reads *_en fields from site.yaml, emits
data-de/data-en attributes on title, description, role, tagline, cta,
tags, section titles, card titles/descriptions, bio, content
- base.html: i18n.js auto-included, title/description get i18n attrs
- All 6 templates: translatable elements get i18n attr placeholders,
footer toggle button with machine-translation disclaimer
- ichbinotto.de pilot: added machine-translation disclaimer per m's request
Templated sites can now be translated by adding _en fields to site.yaml.
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