fix(sync,gui,cli): get a synced folder unstuck when its local copy is gone (#46)

A mirror folder whose files were all gone from this computer stayed in
error for good. The wipe guard rightly refuses to trash the whole folder
on Drive, but nothing got the folder out of that state: a queued switch
to on-demand waits for a pass that ends idle, and its push pass hit the
same guard. Only removing the folder from sync cleared the baseline that
made the empty folder read as "delete everything".

- The push pass for a switch to on-demand forgets the baseline rows of a
  local copy that is gone in full instead of trashing them, so the
  switch goes ahead and the mount shows what Drive has.
- New Request::ResetSyncFolder, `pdfs sync reset ID` and "Sync From
  Scratch…" in a synced folder's menu clear a mirror folder's baseline
  (and a queued switch to on-demand, whose push pass would upload a
  duplicate of every file). The next pass compares both sides as on the
  first sync: one-sided files are copied across, files that differ keep
  both versions, nothing is deleted.
- The wipe guards' messages name the reset; restore logs why it skipped
  a folder.

Two simulations cover it. The on-demand one failed in exactly the
reported state (mirror, pending ondemand, error) before the fix.
All 8 catalogs translated.

docs/CHANGELOG.md

@@ -33,6 +33,11 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
 - **Folder sizes.** **Details** shows how much a folder holds and how many items are in it, as
   Proton Drive counts it, including items in the trash. From a terminal: `pdfs du PATH`.
 
+- **Sync a folder from scratch.** In a synced folder's menu on **Sync → Folders**, **Sync From
+  Scratch…** forgets what was synced before and compares the folder with Proton Drive again. A
+  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`.
+
 ### 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
@@ -48,6 +53,12 @@ scratch (user data in `staging/` and `recovery/` is never touched by this).
 
 ### Fixed
 
+- **A synced folder whose files were all gone from this computer no longer gets stuck** (#46).
+  The sync still refuses to delete everything on Proton Drive, but a switch to online only now
+  goes ahead and shows what Proton Drive has, instead of waiting for good. To download the
+  files again instead, sync the folder from scratch. Restoring folders also logs why it
+  skipped a folder.
+
 - **Saved public links show the name of what they point at**, in the app and in `pdfs bookmarks`,
   instead of "Shared link". For a link with a custom password, the address no longer has the custom
   password stuck to its end, so it matches the link the web shows and the page asks for the