feat: Phase 0 – Gerüst (FastAPI+SQLite, Multi-User-Login, React-App-Shell, Deploy)

Grundgerüst für Certain Finance:
- Backend: FastAPI + SQLAlchemy + SQLite, Alembic-Migrationen (Batch-Mode),
  argon2-Passwort-Hashing, server-seitige Sitzungen im Cookie, Erst-Admin,
  Benutzerverwaltung mit Temporär-Passwort, Einstellungen je Benutzer.
- Ein Prozess, ein Port: uvicorn liefert API (/api) und gebautes SPA aus,
  inkl. SPA-Deeplink-Fallback.
- Frontend: React 18 + Vite + JSX, Design-Tokens (Light/Dark), i18n DE/EN,
  Inline-SVG-Icons (keine Emojis), Login, Passwort-ändern, Dashboard-Platzhalter,
  Benutzer- und Einstellungsseiten.
- Deploy: nativer LXC-Installer + Update-Skript (systemd), env-Vorlage, Doku.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/locales/en.json

@@ -0,0 +1,85 @@
+{
+  "common": {
+    "save": "Save",
+    "cancel": "Cancel",
+    "delete": "Delete",
+    "create": "Create",
+    "edit": "Edit",
+    "loading": "Loading…",
+    "logout": "Log out",
+    "admin": "Administrator",
+    "user": "User",
+    "close": "Close",
+    "retry": "Try again",
+    "actions": "Actions"
+  },
+  "nav": {
+    "overview": "Overview",
+    "accounts": "Accounts",
+    "categories": "Categories",
+    "transactions": "Transactions",
+    "budget": "Budget",
+    "import": "Import",
+    "system": "System",
+    "users": "Users",
+    "settings": "Settings"
+  },
+  "login": {
+    "subtitle": "Please sign in",
+    "username": "Username",
+    "password": "Password",
+    "submit": "Sign in",
+    "error": "Wrong username or password",
+    "expired": "Your session has expired. Please sign in again."
+  },
+  "changepw": {
+    "title": "Change password",
+    "forcedHint": "Please set your own password before continuing.",
+    "current": "Current password",
+    "new": "New password",
+    "repeat": "Repeat new password",
+    "submit": "Save password",
+    "mismatch": "The new passwords do not match.",
+    "saved": "Password changed."
+  },
+  "users": {
+    "title": "Users",
+    "new": "New user",
+    "username": "Username",
+    "displayName": "Display name",
+    "password": "Temporary password",
+    "passwordHint": "The user will be asked to change it on first login.",
+    "role": "Role",
+    "status": "Status",
+    "active": "Active",
+    "inactive": "Disabled",
+    "resetPassword": "Reset password",
+    "deleteConfirm": "Really delete this user?",
+    "created": "User created.",
+    "you": "(you)"
+  },
+  "settings": {
+    "title": "Settings",
+    "baseCurrency": "Base currency",
+    "baseCurrencyHint": "Currency for budget totals and dashboard aggregates.",
+    "locale": "Language",
+    "theme": "Appearance",
+    "themeSystem": "Automatic (system)",
+    "themeLight": "Light",
+    "themeDark": "Dark",
+    "budgetStartDay": "Budget month starts on",
+    "budgetStartDayHint": "Day your budget month starts (e.g. the 25th).",
+    "dateFormat": "Date format",
+    "saved": "Saved.",
+    "languageDe": "German",
+    "languageEn": "English"
+  },
+  "dashboard": {
+    "title": "Overview",
+    "empty": "No cards yet. The dashboard will be built out in a later phase."
+  },
+  "server": {
+    "unreachable": "Server unreachable.",
+    "sessionKept": "Your session is still valid – once the server responds again, it will continue."
+  }
+}