build(editor): blog editor JS build and drift gate

- Private ESM package with exact pins: @tiptap/core, pm, starter-kit,
  extension-table and extension-image 3.31.4; vite 7.3.5, vitest 3.2.7,
  happy-dom 20.11.6 and typescript 5.9.3, the admin SPA toolchain
- vite.config.ts builds assets/src/blogeditor/index.ts into fixed-name
  assets/dist/blogeditor.js and blogeditor.css, minified, and runs vitest
  on happy-dom
- scripts/check-dist.sh rebuilds into a temp dir and fails when assets/dist
  is stale; node_modules is ignored

scripts/check-dist.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Drift gate for the committed Blog Editor bundle (D-16). Rebuilds the element
+# from the committed lockfile into a temporary directory and fails when the
+# result differs from assets/dist, the files admin.go embeds. After changing
+# assets/src, rebuild with `npm run build` and commit assets/dist.
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT"
+
+if [[ ! -d node_modules ]]; then
+  npm ci
+fi
+
+npm run typecheck
+
+TMP="$(mktemp -d)"
+trap 'rm -rf "$TMP"' EXIT
+
+node_modules/.bin/vite build --outDir "$TMP/dist" --emptyOutDir --logLevel warn
+
+if ! diff -r "$TMP/dist" assets/dist; then
+  echo "check-dist: assets/dist is stale; run npm run build and commit assets/dist" >&2
+  exit 1
+fi
+echo "check-dist: assets/dist matches a fresh build"