i18n: complete translations (re-do of stale PR #207)

[rubenvdlinde]

Context

PR #207 (feature/i18n-complete-translations) carried 5 commits:

1. fix: align webpack config and sidebar with shared patterns (overtaken by current App.vue / nc-vue CnAppRoot wiring)
2. fix: settings pattern — use NcAppSettingsDialog modal (overtaken by current dev settings flow)
3. feat(i18n): Fix no-op t(), wrap settings strings, complete translations (l10n keys 134 → 463)
4. refactor: rename #header-actions slot to #actions for consistency (overtaken)
5. fix(i18n): convert title case to sentence case in translation keys

It was closed because the rebase target diverged too far — file deletions (DashboardIndex.vue, Views.vue, MainMenu.vue, etc.) created modify/delete conflicts on virtually every code commit, and many of the 329 added l10n keys reference removed views.

Re-do scope

• Re-audit current src/ for missing t('softwarecatalog', ...) wraps
• Re-translate against current view structure (build keys from the current code, not the March snapshot)
• Sentence-case keys
• Update l10n/en.json, l10n/nl.json, l10n/en.js, l10n/nl.js

References

• Original PR feat(i18n): Fix no-op t(), wrap settings strings, complete translations (93→280 keys) #207
• Translation files at l10n/

Tracked by user feedback rule 'Always file issues for deferred work'.