Add development-scripts agent skill

Ports generic-scripts-module-v1 into a routed skill: module anatomy, shared
loggers/base modules, Taskfile integration, workflows, and pattern decisions.

Fixes a latent defect in the loggers example that silenced all logging in the
module scaffold: loggers/lib/--index-api.sh now sources --env-vars-reader.sh,
and the reader preserves already-exported values so caller overrides still win.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/base/lib/--env-vars-validator.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+# -------------------------------------------------------------------------------------
+# IBM Confidential
+# 6949-70F, 6949-80D
+# © Copyright IBM Corp. 2018, 2024
+# US Government Users Restricted Rights - Use, duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
+# -------------------------------------------------------------------------------------
+
+. ./.scripts/loggers/lib/--index-api.sh
+
+. ./.scripts/base/lib/-ensure-env-var-ibm-user-email.sh
+. ./.scripts/base/lib/-ensure-env-var-ibm-user-api-key.sh
+
+_base_ensureEnvVarIbmUserEmail
+_base_ensureEnvVarIbmUserApiKey