agent: Fix issue where unconfigured MCP extensions would not start server (#33365)

Release Notes:

- agent: Fix an issue where MCP servers that were provided by extensions
would sometimes not start up

crates/extension_host/src/wasm_host/wit/since_v0_6_0.rs

@@ -945,7 +945,10 @@ impl ExtensionImports for WasmState {
                                     .get(key.as_str())
                             })
                             .cloned()
-                            .context("Failed to get context server configuration")?;
+                            .unwrap_or_else(|| {
+                                project::project_settings::ContextServerSettings::default_extension(
+                                )
+                            });
 
                         match settings {
                             project::project_settings::ContextServerSettings::Custom {