fix(sections-editor): translate the autosave failure toast

[pedrofrxncx]

useDebouncedSaveBlock (used by every form-driven block editor — section forms, the SEO editor, SEO sheets) showed a hardcoded English "Save failed: {error}" toast on autosave failure, while every other save-failure toast in this same feature (see sections-editor.tsx, 9+ call sites) goes through t("sectionsEditor.sectionsEditor.saveFailed", { error }), which already has both an en and pt-br translation. A pt-br user editing a section form and hitting a save error would see this one toast in English while every other error toast in the same screen is localized.

Fix: route the same error through the existing useT() + sectionsEditor.sectionsEditor.saveFailed key instead of a template literal. No new translation keys needed — this key already exists and is already used for the identical message elsewhere in the same directory.

Checks run locally:

• bun run fmt
• cd apps/web && bunx tsc --noEmit — clean
• bunx oxlint apps/web/src/components/sections-editor/use-save-block.ts — 0 warnings/errors

No existing test covers this hook's toast wiring (it's UI copy, not a trust boundary), so no test was added per the repo's no-coverage-PR rule. Full CI validates the rest.

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Summary by cubic

Localizes the autosave failure toast in useDebouncedSaveBlock. Previously it showed a hardcoded English "Save failed: {error}"; now it uses t("sectionsEditor.sectionsEditor.saveFailed", { error }) so pt-br users see the translated message.

• Affects all form-driven block editors using useDebouncedSaveBlock (section forms, SEO editor, SEO sheets).
• Reuses existing i18n key; no new translation keys or copy changes.
• No migration or config changes.

^{Written for commit 1f8e5e4. Summary will update on new commits.}