ci: local pre-push hook instead of GH Actions (private repo)

- remove .github/workflows/ci.yml
- add .githooks/pre-push: runs npm run test:all
- git config core.hooksPath .githooks (set)
- docs/DEVELOPMENT.md: document local pipeline

Private repo = no free Actions. Revisit when public.

.githooks/pre-push

@@ -0,0 +1,5 @@
+#!/bin/sh
+# pre-push: run test suites before push. Skip with --no-verify.
+echo "[pre-push] running tests..."
+npm run test:all || { echo "[pre-push] tests failed. push aborted. (skip: git push --no-verify)"; exit 1; }
+exit 0