feat: Strg+S speichert das Dokument direkt als Datei (D74)

Die Geste, die jeder zuerst versucht, tat bisher das Falsche (Browser-Dialog
„Seite speichern"). Jetzt ruft sie saveLocalFile(): mit gemerktem Handle
dialogfrei in dieselbe Datei, sichtbar bestätigt durch einen Petrol-Haken am
Dokumentnamen; ohne Handle wie der Menü-Eintrag. Legenden-Zeile hint_save in
neun Sprachen. Nebenbefund behoben: adoptFile() wartet jetzt auf die aus
IndexedDB zurückgeholten Handles — ein Doppelklick unmittelbar nach dem
App-Start legte sonst ein Duplikat an statt dasselbe Dokument zu
aktualisieren.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/examples/werkbaum.werkbaum

@@ -88,6 +88,7 @@
       - [^] #ed.snaps.manual: Save a state by hand, before a larger change (XS)  %% ten minutes is the wrong beat for that moment
     - [^] #ed.files: Open and save .werkbaum files (S)
       - [^] #ed.files.inplace: Saving writes back into the opened file (S)  %% File System Access, Chromium
+      - [x] #ed.files.ctrls: Ctrl+S saves the document as a file (XS)  %% in place with a remembered handle
     + [^] #ed.fresh: Show what is new since your last visit (S)
       - [^] #ed.fresh.news: A star in the header, with the last few days (S)  %% see D58
     + [?] #ed.percolor: A pastel colour per person (S)
@@ -615,6 +616,12 @@
   handle: saving writes back into the same file, and the same file reopens
   into the same document. Firefox and Safari keep the plain download.
 
+#ed.files.ctrls
+  The save gesture everyone tries first. Without it the browser offers to
+  save the page — the one dialog nobody wants. With a remembered handle it
+  writes straight back in place and flashes the document name as its answer;
+  otherwise it behaves like the menu entry.
+
 #ed.fresh
   For documents that come from outside, nodes that went to production since
   your last visit get a yellow halo. New means live, not "line added" — a line