i18n DE/EN + DossierSettings panel + English file renames

i18n:
- src/i18n/de.json + en.json: 200+ keys covering all main panels
- src/i18n/index.js: t(key, vars) reads window.DOSSIER_LANG
- panel_base.py: injects window.DOSSIER_LANG from dossier_settings.json
- EbenenManager, GeschossManager, AusschnitteApp, LayoutsApp: all
  context menus and main labels use t()

DossierSettings panel:
- DossierSettingsApp.jsx: language toggle (DE/EN pill) + launcher status
- toolbar.py: OPEN_SETTINGS opens new Rhino-hosted satellite window,
  SAVE_LANG writes lang to dossier_settings.json + reloads all panels

File renames (JSX → English):
- ZeichnungsebenenApp → DrawingLevelsApp
- GeschossManager/Dialog/Settings → Floor*
- AusschnitteApp/Settings → Viewports*
- EbenenManager/Settings → Layer*
- GestaltungApp → StylesApp, OberleisteApp → ToolbarApp
- WerkzeugeApp → ToolsApp, DimensionenApp → DimensionsApp
- MassstabApp → ScaleApp, KameraApp → CameraApp
- MasseSettingsApp → UnitsSettingsApp
- ConfirmDeleteEbene → ConfirmDeleteLayer
- AusschnittLayerDialog → ViewportLayerDialog

Python module renames:
- rhinopanel.py → layers_panel.py
- oberleiste.py → toolbar.py
- gestaltung.py → styles.py
- werkzeuge.py → tools.py
- dimensionen.py → dimensions.py
- startup.py _MODULE_TO_PY updated, all cross-imports fixed

src/components/ConfirmDeleteLayer.jsx

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+// Copyright (C) 2026 Karim Gabriele Varano
+import { useState } from 'react'
+import Icon from './Icon'
+import { BarToggle, BarCombo } from './BarControls'
+
+export default function ConfirmDeleteEbene({ ebene, otherEbenen, onConfirm, onCancel }) {
+  const [target, setTarget] = useState(otherEbenen[0]?.code ?? '_delete')
+  const isDelete = target === '_delete'
+
+  return (
+    <div style={{
+      position: 'absolute', inset: 0, zIndex: 200,
+      background: 'var(--bg-overlay)',
+      display: 'flex', alignItems: 'center', justifyContent: 'center',
+      padding: 16,
+    }}>
+      <div style={{
+        background: 'var(--bg-dialog)',
+        border: '1px solid var(--border)',
+        borderRadius: 'var(--r-lg)',
+        boxShadow: 'var(--shadow-3)',
+        width: 320, maxWidth: '100%',
+        display: 'flex', flexDirection: 'column',
+        overflow: 'hidden',
+      }}>
+        <div style={{ padding: '16px 18px 6px', display: 'flex', gap: 10, alignItems: 'flex-start' }}>
+          <span style={{
+            display: 'inline-flex', alignItems: 'center', justifyContent: 'center',
+            width: 28, height: 28, borderRadius: '50%',
+            background: 'var(--warn-dim)', color: 'var(--warn)',
+            flexShrink: 0,
+          }}>
+            <Icon name="warning" size={18} />
+          </span>
+          <div>
+            <div style={{ fontWeight: 600, fontSize: 13, color: 'var(--text-primary)', marginBottom: 2 }}>
+              Ebene löschen
+            </div>
+            <div style={{ fontSize: 11, color: 'var(--text-secondary)', lineHeight: 1.5 }}>
+              <b>{ebene.code}_{ebene.name}</b> wird in allen Zeichnungsebenen entfernt.
+            </div>
+          </div>
+        </div>
+
+        <div style={{ padding: '10px 18px 14px', display: 'flex', flexDirection: 'column', gap: 6 }}>
+          <span className="label-xs">Inhalte auf der Ebene</span>
+          <BarCombo stretch
+            value={target}
+            onChange={(v) => setTarget(v)}>
+            {otherEbenen.map(e => (
+              <option key={e.code} value={e.code}>→ Verschieben nach {e.code}_{e.name}</option>
+            ))}
+            <option value="_delete">⚠  Inhalte ebenfalls löschen</option>
+          </BarCombo>
+        </div>
+
+        <div style={{
+          display: 'flex', gap: 6, padding: '10px 14px',
+          justifyContent: 'flex-end',
+          borderTop: '1px solid var(--border-light)',
+          background: 'var(--bg-section)',
+        }}>
+          <BarToggle label="Abbrechen" onClick={onCancel} />
+          <BarToggle
+            label="Löschen"
+            active
+            onClick={() => onConfirm(isDelete ? null : target)}
+          />
+        </div>
+      </div>
+    </div>
+  )
+}