bug#81645: 32.0.50; Annotations break *Completions* navigation in vertical format

0. emacs -Q
1. (setopt completions-format 'vertical)
2. Sanity check: Typing `M-x auto- TAB' pops up the *Completions* buffer
   and you can navigate up and down through each column by typing
   `M-<DOWN>' and `M-<UP>' with wrapping from the last to the first
   candidate and vice versa.
3. Now type `M-x abbrev- TAB', then repeatedly type `M-<DOWN>': after
   the last candidate point wraps to the second instead of the first
   candidate.
4. Now type `M-x dabbrev- TAB'.  Now typing `M-<DOWN>' once moves to
   last candidate, but repeating `M-<DOWN>' does not move point (in
   particular, no wrapping).  Now typing `M-<UP>' moves point back to
   the first candidate, but typing `M-<UP>' again move point not to the
   beginning of the last candidate but to the middle of the annotation
   "(M-/)" affixed to the candidate.

The problems in 3 and 4 are due to the annotations in the *Completions*
buffer.  The attached patch fixes these problems, so that navigation in
3 and 4 work as in 2 according to my testing.  I think this patch should
be applied to the release branch because the type of navigation in
vertical format illustrated by 2 was introduced in Emacs 31 by commit
77ca60b48d01, which, however, failed to take annotations into account.


In GNU Emacs 32.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version
 3.24.52, cairo version 1.18.4) of 2026-08-14 built on strobelfs
Repository revision: cb22cfe1414bc3aa5a0e0b54f41f5b3453cb1f01
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101024
System Description: Linux From Scratch r13.0-156

Configured using:
 'configure -C --with-native-compilation=no 'CFLAGS=-Og -g3'
 PKG_CONFIG_PATH=/opt/qt6/lib/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
LCMS2 LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP
SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM
XINERAMA XINPUT2 XPM XRANDR GTK3 ZLIB

diff --git a/lisp/simple.el b/lisp/simple.el
index 1f7d57f299a..137734d9f03 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -10176,8 +10176,11 @@ last-completion
           (last-col (progn
                       (first-completion)
                       (goto-char (pos-eol))
-                      (goto-char (previous-single-property-change
-                                  (point) 'mouse-face))
+                      ;; Go to the beginning of the candidate.  We loop
+                      ;; to move past any completion annotations.
+                      (while (not (get-text-property (point) 'mouse-face))
+                        (goto-char
+                         (previous-single-property-change (point) 'mouse-face)))
                       (current-column))))
       (if (zerop last-col)
           ;; If there is only one column of completions, the last