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

rhino/panel_base.py

@@ -20,6 +20,21 @@ import scriptcontext as sc
 
 _HERE  = os.path.dirname(os.path.abspath(__file__))
 _DIST  = os.path.join(_HERE, "..", "dist", "index.html")
+_SETTINGS_PATH = os.path.expanduser(
+    "~/Library/Application Support/ch.gabrielevarano.Dossier/dossier_settings.json")
+
+
+def _read_lang():
+    """Liest die UI-Sprache aus dossier_settings.json. Default: 'de'."""
+    try:
+        if os.path.isfile(_SETTINGS_PATH):
+            with open(_SETTINGS_PATH, "rb") as f:
+                d = json.loads(f.read().decode("utf-8"))
+            lang = d.get("lang", "de")
+            return lang if lang in ("de", "en") else "de"
+    except Exception:
+        pass
+    return "de"
 
 
 # --- Timing-Instrumentierung ------------------------------------------------
@@ -317,7 +332,8 @@ def load_inline(wv, mode, params=None):
         _INLINE_TEMPLATE = (sig, tmpl)
 
     # Per-Mount: nur das Mode-Script-Snippet bauen
-    parts = ['window.PANEL_MODE="{}";'.format(mode)]
+    parts = ['window.PANEL_MODE="{}";'.format(mode),
+             'window.DOSSIER_LANG="{}";'.format(_read_lang())]
     if params is not None:
         try:
             parts.append('window.PANEL_PARAMS=' + json.dumps(params, ensure_ascii=False) + ';')