test(acceptance): cover copy, folder size, link updates and sync recovery

New cases for what 3.6.0 adds:

- copy_file_range over several calls, into the middle of a file, past
  its end, at the source's end, and from a file whose writes are not
  released yet; on a live mount also read back from Drive.
- pdfs copy of a tree and of a file beside itself, read back as listed
  and after a refresh, with nothing queued; refused while a file has
  writes Drive lacks, and never the version before a save (B256).
- pdfs du counts every item below a folder, trash included.
- pdfs public-link update keeps the URL and the options it was not
  asked to change, and refuses a link id that is not the folder's.
- In a sync folder of their own: Sync From Scratch changes nothing that
  already matched, and an emptied mirror folder still switches to
  on-demand with every file intact on Drive (B255).

docs/TESTING.md gains a checklist for the new screens in the app. The
CHANGELOG moves these into 3.6.0, which is not tagged yet.

docs/CHANGELOG.md

@@ -11,7 +11,7 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
 
 ## [Unreleased]
 
-## [3.6.0] — 2026-10-26
+## [3.6.0] — 2026-10-27
 
 Schema: **44**, unchanged.
 
@@ -46,6 +46,9 @@ Schema: **44**, unchanged.
   file on one side only is copied to the other, and a file that differs keeps both versions.
   Nothing is deleted. From the terminal: `pdfs sync reset ID`.
 
+- **`--json` for `pdfs members`, `pdfs du` and `pdfs public-link create` / `update`**, so scripts
+  can read a link's id, role, password flag and expiry, and a folder's size and item count.
+
 ### Changed
 - **Copying a file inside the mount is faster** when the computer already has the file, for
   example with `cp` or a file manager: the copy is made on this computer, about four times
@@ -58,6 +61,10 @@ Schema: **44**, unchanged.
   pages for files, synced folders, Photos, sharing, computers, and the launcher and tray.
   Installation puts the COPR repository first for Fedora and explains updating and uninstalling
   for each kind of package. Each release publishes `docs/` to the wiki.
+- **Acceptance cases for the 3.6.0 features:** `copy_file_range` over several calls and at
+  offsets, `pdfs copy` (including B256), `pdfs du`, `pdfs public-link update`, Sync From Scratch,
+  and the switch of an emptied mirror folder to on-demand (B255). `docs/TESTING.md` lists what to
+  check by hand in the app.
 
 ### Fixed