feat: add per-pane default foreground/background color support (#4737)

* feat: add per-pane default foreground/background color support

Add per-pane default foreground and background colors, configurable
through four surfaces:

- OSC 10/11 escape sequences (set/query) and OSC 110/111 (reset)
- CLI action: zellij action set-pane-color --pane-id <id> --fg/--bg
- Layout config: default_fg/default_bg properties on pane nodes
- Plugin API: set_pane_color() SDK function and PaneInfo read-side

Colors are applied at render time as a fallback when cells have no
explicit foreground/background, without mutating stored grid data.

Closes #4712

* refactor: address review feedback for pane color support

- Extract adjust_styles_for_custom_bg_fg in output/mod.rs
- Move color parsing (xparse_color) from tab into Grid
- Move color serialization (ansi_code_to_color_string) into Grid
- Pane trait now uses Option<String> for color getters/setters
- Add colors to session serialization (dump-layout)
- Add default_fg/default_bg to protobuf IPC schema to fix
  layout-in-session color loss
- Update example layout with tab-bar and status-bar

* fix stack overflow and ordering

* rustfmt

* update e2e snapshots

---------

Co-authored-by: Karl Bunch <karl@karlbunch.com>
Co-authored-by: Aram Drevekenin <aram@poor.dev>

1 files changed, 8 insertions, 0 deletions

diff --git a/zellij-utils/src/plugin_api/plugin_command.proto b/zellij-utils/src/plugin_api/plugin_command.proto
index 7ba3aabe..53e9d729 100644
--- a/zellij-utils/src/plugin_api/plugin_command.proto
+++ b/zellij-utils/src/plugin_api/plugin_command.proto
@@ -198,6 +198,7 @@ enum CommandName {
   OpenEditPaneInPlaceOfPaneId = 203;
   HideFloatingPanes = 204;
   ShowFloatingPanes = 205;
+  SetPaneColor = 206;
 }
 
 message PluginCommand {
@@ -345,6 +346,7 @@ message PluginCommand {
     OpenEditPaneInPlaceOfPaneIdPayload open_edit_pane_in_place_of_pane_id_payload = 154;
     HideFloatingPanesPayload hide_floating_panes_payload = 155;
     ShowFloatingPanesPayload show_floating_panes_payload = 156;
+    SetPaneColorPayload set_pane_color_payload = 157;
   }
 }
 
@@ -1212,3 +1214,9 @@ message HideFloatingPanesResponse {
     string error = 2;
   }
 }
+
+message SetPaneColorPayload {
+  PaneId pane_id = 1;
+  optional string fg = 2;
+  optional string bg = 3;
+}