fix: clarify module post-install script errors as non-fatal warnings

Change error display from log.error to log.warn and explain that the
module was installed successfully — only the optional post-install
script could not run. Prevents users from thinking the module
installation itself failed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/cli/installers/lib/modules/manager.js

@@ -1328,7 +1328,10 @@ class ModuleManager {
         }
       }
     } catch (error) {
-      await prompts.log.error(`Error running module installer for ${moduleName}: ${error.message}`);
+      await prompts.log.warn(
+        `Post-install script for ${moduleName} could not run: ${error.message}\n` +
+          `  The module itself was installed successfully. The post-install script is optional.`,
+      );
     }
   }