docs: correct the shortcut and help entry points, and the rate example

The whole-branch review found README describing a toolbar "?" button that
does not exist, Ctrl+? for an overview bound to Ctrl+/, bare `e` for an
export bound to Ctrl+E, and a help window that opens "on the page nearest
to what the user was doing" when it unconditionally selects Overview. All
four would send a reader looking for something that is not there. The key
table also claimed to be full while omitting F1, Ctrl+/ and Ctrl+Q, and
did not say that `f` is the plot's own key rather than an app accelerator.

format_rate() is %.3g, so it prints "10 kS/s"; the two doc comments in
status_text.hpp and the example in help page 01 still said "10.0 kS/s" —
the same error already corrected in 14-status.txt and CLAUDE.md, left in
the header that declares the function and in a second user-facing page.

close_help_windows()'s comment described only gtk_window_close(), and
show_shortcuts()'s called the overview "hand-rolled"; the Adwaita rework
made one half-true and the other false.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/help/01-overview.txt

@@ -23,4 +23,4 @@ one on in the side panel (<tt>s</tt>) and drag it onto a row.
 <b>Example</b>
 
 A 3-signal source at 10 kS/s with a 200 MB buffer holds 1677 s of history. Enable all three,
-drop them on row 1, and the status bar reads <tt>● live · 10.0 kS/s · 2 s window</tt>.
+drop them on row 1, and the status bar reads <tt>● live · 10 kS/s · 2 s window</tt>.

src/help_window.hpp

@@ -29,12 +29,14 @@ struct HelpReport {
 HelpReport help_self_check();
 
 /// The shortcut overview: the application accelerators and the plot's own interactions,
-/// in the sections the tables name. Hand-rolled because GtkShortcutsWindow is deprecated
-/// as of GTK 4.18 and this project builds warning-free.
+/// in the sections the tables name. An AdwShortcutsDialog, because GtkShortcutsWindow is
+/// deprecated as of GTK 4.18 and this project builds warning-free.
 void show_shortcuts(GtkWindow* parent);
 
-/// Closes whichever of the three windows are open, via gtk_window_close() so the
-/// close-request handlers run and the pointers are nulled. Used by the probe.
+/// Closes whichever of the three windows are open. The About dialog and the help window are
+/// GtkWindows and close with gtk_window_close(), so their close-request handlers run; the
+/// shortcut overview is an AdwDialog and closes with adw_dialog_close(), which emits ::closed.
+/// Either way the file-scope pointer is nulled by the handler. Used by the probe.
 void close_help_windows();
 
 }  // namespace udpscope

src/status_text.hpp

@@ -46,7 +46,7 @@ struct StatusSnapshot {
   int reconnects = 0;
 };
 
-/// The bar: "live · 10.0 kS/s · 2 s window", plus " · event 4.2 s ago" in trigger mode and
+/// The bar: "live · 10 kS/s · 2 s window", plus " · event 4.2 s ago" in trigger mode and
 /// nothing else ever. The badge glyph is a separate widget and is not part of this string.
 std::string format_glance(const StatusSnapshot& s);
 
@@ -55,7 +55,8 @@ std::string format_glance(const StatusSnapshot& s);
 /// their order must not change without updating it.
 std::string format_detail(const StatusSnapshot& s);
 
-/// A sample rate as "10.0 kS/s". Moved here from ui.cpp, which still calls it.
+/// A sample rate as "10 kS/s" — `%.3g`, so a trailing zero is dropped and the field's width
+/// cannot track the stream. Moved here from ui.cpp, which still calls it.
 std::string format_rate(double hz);
 
 /// An elapsed time, stepping to a coarser unit rather than growing digits, so its width