Stempelstile-Tab in ProjectSettings (Manager analog Raumstile)

Beide Stempel-Familien (Raum-Stempel + Bilanz-Stempel) sind jetzt
konsistent verwaltbar in den Project-Settings.

Backend:
- elemente.py: DUPLICATE_STEMPEL_STIL + REORDER_STEMPEL_STILE handlers
- rhinopanel.py ProjectSettings-Bridge:
  - stempel_stile in params (initial)
  - 4 neue dispatch-Handler (SAVE/DELETE/DUPLICATE/REORDER_STEMPEL_STIL)
  - direkter Dispatch zu elemente.load/save_stempel_stile (kein Roundtrip)
  - STEMPEL_STILE_UPDATED-Message nach jeder Op

Frontend:
- rhinoBridge.js: reorderStempelStile + duplicateStempelStil exports
- ProjectSettingsDialog:
  - Neuer Tab "Stempelstile" parallel zu "Raumstile"
  - Drag-Reorder via HTML5 native, Inline-Rename, Duplicate, Delete
  - Mini-Preview: Header + Anzahl aktiver Show-Flags
  - Name wird mit Font/Bold/Italic des Stils gerendert als Vorschau

src/lib/rhinoBridge.js

@@ -265,6 +265,10 @@ export function deleteStempelStil(id) { send('DELETE_STEMPEL_STIL', { id }) }
 export function applyStempelStil(stilId, ids) {
   send('APPLY_STEMPEL_STIL', { stilId, ids })
 }
+export function reorderStempelStile(ids) { send('REORDER_STEMPEL_STILE', { ids }) }
+export function duplicateStempelStil(id, newName) {
+  send('DUPLICATE_STEMPEL_STIL', { id, newName })
+}
 export function setSectionStyle(enabled, source, color, pattern, scale, rotation,
                                 opts = {}) {
   send('SET_SECTION_STYLE', {