patches: fix 2 blockers from Opus review

BLOCKER #1: accessibilityUpdating flag exception safety.
A Lisp signal (longjmp) during postAccessibilityUpdates left
the re-entrance flag permanently YES, suppressing all future
AX notifications → VoiceOver goes silent randomly.
Fix: specpdl unwind protection (record_unwind_protect_ptr)
resets the flag on any longjmp. All 3 exit points use unbind_to.

BLOCKER #2: static struct buffer *lastBuffer dangling pointer.
Raw C pointer to buffer struct has no GC protection. After
kill-buffer, the pointer dangles.
Fix: file-scope Lisp_Object lastChildFrameBuffer with staticpro.
EQ comparison instead of pointer equality.

Also: revert accidental em-dash → triple-dash in title bar (0007),
fix README factual error (BUF_OVERLAY_MODIFF cache key).

patches/0007-ns-announce-overlay-completion-candidates-for-VoiceO.patch

@@ -1,4 +1,4 @@
-From bb69ef51db4c87dfe88861927264121f95fc627f Mon Sep 17 00:00:00 2001
+From 6e907a1000a8b138976d6a906e40449fdf1a61c5 Mon Sep 17 00:00:00 2001
 From: Martin Sukany <martin@sukany.cz>
 Date: Sat, 28 Feb 2026 14:46:25 +0100
 Subject: [PATCH 1/2] ns: announce overlay completion candidates for VoiceOver
@@ -52,8 +52,8 @@ Independent overlay branch, BUF_CHARS_MODIFF gating, candidate
 announcement with overlay Zoom rect storage.
 ---
  src/nsterm.h |   3 +
- src/nsterm.m | 335 +++++++++++++++++++++++++++++++++++++++++++++------
- 2 files changed, 300 insertions(+), 38 deletions(-)
+ src/nsterm.m | 331 +++++++++++++++++++++++++++++++++++++++++++++------
+ 2 files changed, 298 insertions(+), 36 deletions(-)
 
 diff --git a/src/nsterm.h b/src/nsterm.h
 index 51c30ca..5c15639 100644
@@ -77,7 +77,7 @@ index 51c30ca..5c15639 100644
    BOOL font_panel_active;
    NSFont *font_panel_result;
 diff --git a/src/nsterm.m b/src/nsterm.m
-index 1780194..6efeb1d 100644
+index 1780194..143e784 100644
 --- a/src/nsterm.m
 +++ b/src/nsterm.m
 @@ -3258,7 +3258,12 @@ ns_draw_window_cursor (struct window *w, struct glyph_row *glyph_row,
@@ -570,22 +570,6 @@ index 1780194..6efeb1d 100644
     Methods are kept here (same .m file) so they access the ivars
     declared in the @interface ivar block.  */
  @implementation EmacsAccessibilityBuffer (InteractiveSpans)
-@@ -10520,13 +10779,13 @@ ns_in_echo_area (void)
-         if (old_title == 0)
-           {
-             char *t = strdup ([[[self window] title] UTF8String]);
--            char *pos = strstr (t, "  —  ");
-+            char *pos = strstr (t, "  ---  ");
-             if (pos)
-               *pos = '\0';
-             old_title = t;
-           }
-         size_title = xmalloc (strlen (old_title) + 40);
--	esprintf (size_title, "%s  —  (%d × %d)", old_title, cols, rows);
-+	esprintf (size_title, "%s  ---  (%d × %d)", old_title, cols, rows);
-         [window setTitle: [NSString stringWithUTF8String: size_title]];
-         [window display];
-         xfree (size_title);
 @@ -11922,7 +12181,7 @@ ns_ax_collect_windows (Lisp_Object window, EmacsView *view,
  
    if (WINDOW_LEAF_P (w))