docs: migrate README to API-Doc-Convention (S2-cascade.libs)

Restructured per ADR-0038: Abstract + bold-list Badges + Topology H2
+ H3-API-Subsections (one per public function) + Conventions/Consumer
pattern/CHANGELOG/References.

Topology auto-populated via Sporel.exe --lint --fix. Pre-commit hook
installed via --install-hooks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.githooks/pre-commit

@@ -0,0 +1,13 @@
+#!/bin/sh
+# Sporel API-Doc-Convention pre-commit hook.
+SPOREL_EXE="${SPOREL_EXE:-$(command -v Sporel.exe 2>/dev/null || command -v sporel 2>/dev/null)}"
+if [ -z "$SPOREL_EXE" ]; then
+  echo "INFO: Sporel.exe not on PATH. Skipping lint." >&2
+  exit 0
+fi
+"$SPOREL_EXE" --lint="$(pwd)" --fix
+RC=$?
+if git diff --cached --name-only | grep -qx 'README.md'; then
+  git add README.md
+fi
+exit $RC