feat: add German language support (DE/EN/FR)

[mkocustos]

Summary

• Adds full German (de) translations for all namespaces: common, auth, recipes, editor, importRecipe, settings, privacy
• Adds a german key to the existing English and French settings translations
• Language auto-detected from device locale: German device → Deutsch, English device → English, everything else → Français (existing fallback unchanged)
• Language remains manually overridable in Settings — a new third segment Deutsch appears alongside Français and English
• Extends the language type from "fr" | "en" to "fr" | "en" | "de" in PreferencesProvider and persists the selection via AsyncStorage

Files changed

File	Change
src/i18n/index.ts	German translation block; german key added to EN + FR; updated language detection
src/features/preferences/PreferencesProvider.tsx	Type extended to "fr" | "en" | "de"; init and validation logic updated
src/screens/SettingsScreen.tsx	Third language option (Deutsch) added to SegmentedControl

Bug fix: auto-detection overridden by stale AsyncStorage value

Problem: On first launch after installing the update, the app could show the wrong language (e.g. English) even on a German device. The PreferencesProvider reads any previously stored language from AsyncStorage and applies it unconditionally — including values written by an older version of the app that had no German support. Since those older values were never explicitly chosen by the user (they were set automatically), the stored "en" would silently override the device locale.

Fix: A separate preferences.language.userSet flag is now written to AsyncStorage only when the user actively changes the language via setLanguage. On startup, the stored language is only restored if this flag is true. If no explicit choice has been recorded, the device locale is used as intended.

Testing

Tested on Apple iPhone with Expo Go — app correctly launches in German on a German-locale device. Language switching in Settings also works as expected.

This implementation was generated with Claude Code.

[mkocustos]

Note: PR #18 adds a language switcher directly to the login screen (fixes #16). It is based on main and currently typed as "fr" | "en". Once this PR is merged, the login screen picker should also be updated to include "de" — a one-line type change in LoginScreen.tsx:

<SegmentedControl<"fr" | "en" | "de">

along with the additional option:

{ label: t("settings.german"), value: "de" }

[Logarex]

Thank you so much for taking the time to add the German translation.

Your fix for the AsyncStorage stale value overriding the system locale is brilliant. The userSet flag makes perfect sense and is a much cleaner way to handle the fallback logic.

I just pulled the branch locally and tested it on my simulator: everything works flawlessly. The language switch is smooth and the persistence bug is fully resolved.

Merging this right away. Thanks again for this massive contribution to AvoCook!