sl0p: optionally hide the 'Pane #N' placeholder title

`ui { pane_frames { hide_default_pane_names true } }`, default false.

A pane now shows no title at all until something actually names it: the user
renaming it (including by double-clicking the title row) or the running
program setting a title. Upstream always shows an auto-generated 'Pane #N'.

Implemented by tracking whether pane_title is still the constructor's
placeholder, NOT by matching the string: a program that legitimately titles
itself 'Pane #3' must not be mistaken for an unnamed pane. set_title clears
the flag, since something then chose that title.

current_title reads the option at render time rather than baking an empty
title in at construction, so it hot-reloads and turning the option back off
restores the placeholder on existing panes.

Display precedence is unchanged and now explicit in the code:
    user-given name > title set by the running program > placeholder

render_terminal_title already fell back to an empty string rather than the
placeholder, so the terminal WINDOW title is unaffected.

Empty titles were already handled by the frame renderer
(render_title_left_side returns None for an empty title), including the
sl0p centred/right alignment path.

Baselines held: zellij-server 1436/30, zellij-utils 436/5.

1 files changed, 6 insertions, 3 deletions

diff --git a/zellij-server/src/tab/mod.rs b/zellij-server/src/tab/mod.rs
index 18945a68..08ee4bc9 100644
--- a/zellij-server/src/tab/mod.rs
+++ b/zellij-server/src/tab/mod.rs
@@ -778,6 +778,7 @@ pub trait Pane {
         _gap_y: usize,
         _padding: zellij_utils::data::PanePadding,
         _inactive_grayscale: u8,
+        _hide_default_pane_names: bool,
     ) {
     }
     fn set_should_be_suppressed(&mut self, _should_be_suppressed: bool) {}
@@ -7448,18 +7449,20 @@ impl Tab {
         gap_y: usize,
         padding: zellij_utils::data::PanePadding,
         inactive_grayscale: u8,
+        hide_default_pane_names: bool,
     ) {
         self.style.pane_title_alignment = title_alignment;
         self.style.pane_gap_x = gap_x;
         self.style.pane_gap_y = gap_y;
         self.style.pane_padding = padding;
         self.style.inactive_pane_grayscale = inactive_grayscale;
+        self.style.hide_default_pane_names = hide_default_pane_names;
         self.floating_panes
-            .update_pane_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale);
+            .update_pane_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale, hide_default_pane_names);
         self.tiled_panes
-            .update_pane_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale);
+            .update_pane_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale, hide_default_pane_names);
         for (_, pane) in self.suppressed_panes.values_mut() {
-            pane.update_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale);
+            pane.update_frame_layout(title_alignment, gap_x, gap_y, padding, inactive_grayscale, hide_default_pane_names);
         }
     }
     pub fn update_arrow_fonts(&mut self, should_support_arrow_fonts: bool) {