Add /debug-config slash command (#10642)

<img width="409" height="175" alt="image"
src="https://github.com/user-attachments/assets/76efe9c5-8375-4af3-b6af-bd9e162c1bc3"
/>

codex-rs/tui/src/slash_command.rs

@@ -33,6 +33,7 @@ pub enum SlashCommand {
     Diff,
     Mention,
     Status,
+    DebugConfig,
     Mcp,
     Apps,
     Logout,
@@ -63,6 +64,7 @@ impl SlashCommand {
             SlashCommand::Mention => "mention a file",
             SlashCommand::Skills => "use skills to improve how Codex performs specific tasks",
             SlashCommand::Status => "show current session configuration and token usage",
+            SlashCommand::DebugConfig => "show config layers and requirement sources for debugging",
             SlashCommand::Ps => "list background terminals",
             SlashCommand::Model => "choose what model and reasoning effort to use",
             SlashCommand::Personality => "choose a communication style for Codex",
@@ -118,6 +120,7 @@ impl SlashCommand {
             | SlashCommand::Mention
             | SlashCommand::Skills
             | SlashCommand::Status
+            | SlashCommand::DebugConfig
             | SlashCommand::Ps
             | SlashCommand::Mcp
             | SlashCommand::Apps