Add initial scripts and project conventions

.shellcheckrc

@@ -0,0 +1,8 @@
+# shellcheck config — applies to every script in this repo via `shellcheck`
+# run from the repo root. See AGENTS.md for the mandatory-shellcheck rule.
+
+# Follow sourced files (needed so shellcheck resolves lib/common.sh
+# correctly instead of flagging unknown functions as undefined).
+external-sources=true
+
+shell=bash