Fix/no ref/german translations

[jufickel-b]

Summary

Completes the German (de) translation, bringing it to full key parity with English.

• Translated all remaining untranslated strings in packages/core/src/i18n/locales/de.ts (previously ~1468 of the English key count, now 2474 — full coverage).
• Used the formal capitalized "Du" address throughout, consistent with the existing translation style.
• Raised de's translatedKeyFloor in i18n-locales.ts from 1468 to 2474 and updated getLocaleCoverageTier expectations in index.test.ts so de is now reported as full coverage instead of partial.
• Added de (and its allowed loanword/internationalism list, e.g. "Status", "Details", "Version", "System", "E-Ink", "Sepia") to allowedEnglishMirrorKeysByLocale in locale-quality.ts, documenting which keys are intentionally left identical to English.
• Adjusted starter seed strings (starter-seed-strings.ts) to consistently use "Eingang" instead of "Posteingang" for the German "Inbox" term.

Related issue

No related issue — this gap was found and fixed directly while reviewing German (de) locale coverage; no GitHub issue was filed for it.

Testing

• npx vitest run src/i18n in packages/core — 6 test files, 178 tests, all passing (includes locale-parity.test.ts and index.test.ts coverage-tier assertions).
• Manually verified in the running desktop app UI.

Screenshots / recordings

N/A (translation-only change, no UI/layout changes).

Checklist

• I have signed the Contributor License Agreement (CLA)
• I have tested this change locally
• I linked the relevant issue (or explained why there isn't one)
• I added or updated tests/docs if needed

[CLAassistant]

All committers have signed the CLA.

[dongdongbh]

Needs changes

The translation is close, and the floor bump, the mirror allow-list and the tier test change are right. Two strings are functionally wrong and a dozen carry grammar or consistency slips. Please fix these in de.ts before it lands.

Functional:

• agenda.maxFocusItems: {{count}} was replaced by the word "drei". The focus limit is a user setting, so the label is wrong for every value except 3. Keep the placeholder: Max. {{count}} Fokus-Element(e) or similar.
• dailyReview.focusDesc: the English says "Optional: mark tasks to keep visible in Focus today". The German drops "optional" and hardcodes a limit of three. Something like Optional: Aufgaben markieren, die heute im Fokus sichtbar bleiben sollen.

Wording:

• projects.reviewAt: Datum überprüfen reads as a command. It is the "Review Date" field label, e.g. Überprüfungsdatum.
• quickAdd.pastedImageSaving: Hände Bild an… should be Hänge Bild an….
• settings.speechModeTranscript: Nur transkripieren should be Nur transkribieren, matching settings.speechModeHint.
• review.allDoneDesc: stray "für" in Du bist für bereit für die kommende Woche.
• review.projectsHint: abgeschlossen Projekte should be abgeschlossene Projekte.
• next.warningHint: eine besser Übersicht should be eine bessere Übersicht.
• calendar.overlapWarning: mit einem bestehendem Termin should be mit einem bestehenden Termin.
• inbox.waitingHint: um sich zu erinnern, auf was Du wartest should be um Dich zu erinnern, worauf Du wartest, as process.waitingForDesc already has it.
• inbox.waitingPlaceholder and process.waitingPlaceholder: Jonathan's should be Jonathans.
• review.inboxStepDesc: the English says "Clarify and organize", and Clarify is the GTD step name. durchsehen means look through; Deine Eingangs-Einträge klären und organisieren. keeps the term and the linking s.

Consistency:

• nav.board says Spaltenansicht while board.title and tab.board say Tafelansicht / Tafel. Pick one.
• next.noTasks calls the list Zu erledigen while status.todo, list.todo and board.todo call it Zu tun.
• Button labels such as settings.checkForUpdates, settings.checkStoreUpdates, settings.attachmentsCleanupRun and settings.dropboxDisconnect became commands to the user (Suche nach…, Überprüfe…, Führe… durch, Trenne…). German UI buttons use the infinitive: Nach Aktualisierungen suchen, Microsoft Store prüfen, Bereinigung ausführen, Dropbox trennen.
• Capitalization of the informal address: your new lines use "Du", while about 57 pre-existing lines you did not touch (mindSweep.*, starter.*, onboarding.*, calendar.openFromCalendarApp) use lowercase "du", so the file now mixes both. Since you are in there anyway, please unify to one form; capitalized "Du" is fine.

One decision on our side: the rename from "Posteingang" to "Eingang" is fine. Things, Todoist and OmniFocus use it in German. I will update the German docs after the merge, so leave them alone.