fix(repl): offer prompts in .list tab completion and rename its listing helpers

MCP prompts are live, server-owned catalog entries, not managed assets;
list_prompt_assets/prompt_asset_rows implied otherwise and are now
list_mcp_prompts/mcp_prompt_rows. The .list completer was also missing
the prompts kind that the usage string and unknown-kind error advertise.

src/repl/mod.rs

@@ -1251,7 +1251,7 @@ pub async fn run_repl_command(
             },
             ".list" => match args.map(str::trim) {
                 Some("prompts") => {
-                    ctx.list_prompt_assets().await?;
+                    ctx.list_mcp_prompts().await?;
                 }
                 Some(args) => {
                     ctx.list_assets(args)?;