docs: PWA-Dateihandling als Plan-Knoten (#bld.pwa.files)

Installierte App registriert sich für .werkbaum (file_handlers), Doppelklick
öffnet mit fertigem Handle aus der launchQueue, Speichern ohne Dialog —
hängt an der vorhandenen Stufe-2-Mechanik (:#ed.files.inplace).

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

docs/examples/werkbaum.werkbaum

@@ -103,6 +103,7 @@
       - [ ] #bld.pwa.manifest: A manifest with name, icons and standalone display (XS)
       - [ ] #bld.pwa.sw: A service worker that serves the app offline (S)  %% one file to cache
       - [ ] #bld.pwa.update: The reload notice moves into the worker (S)  %% see D45
+      - [ ] #bld.pwa.files: Double-click a .werkbaum file, save without any dialog (S) :#ed.files.inplace  %% file_handlers + launchQueue
     - [-] #bld.ghpages: Deploy through a gh-pages branch (S)  %% GitHub Actions instead
     - [-] #bld.gfonts: Fonts from Google (XS)  %% self-hosted, no third-party request
   - [ ] #be: Backend (XL)
@@ -685,6 +686,14 @@
   it decides what gets served, so "the running build against the one the
   server sends" is no longer the same comparison.
 
+#bld.pwa.files
+  The installed app registers for the .werkbaum extension: double-clicking a
+  file in the OS opens it here, with a ready file handle from the launch
+  queue. Together with the persistent write permission an installed app can
+  hold, editing becomes open, type, save — no dialog at all. The saving
+  mechanics already exist; what is missing is the manifest entry and the
+  launch-queue receiver. Chromium only.
+
 #bld.ghpages
   Rejected: the official Actions route needs no extra branch and no deploy
   key.