refactor(baoyu-translate): replace remark/unified with markdown-it for chunk parsing

Simplifies dependencies and adds main.ts CLI entry point with exported
functions for programmatic reuse.

skills/baoyu-translate/scripts/main.ts

@@ -0,0 +1,55 @@
+#!/usr/bin/env bun
+import path from "node:path"
+import process from "node:process"
+import { runChunkCli } from "./chunk.js"
+
+function formatScriptCommand(fallback: string): string {
+  const raw = process.argv[1]
+  const displayPath = raw
+    ? (() => {
+        const relative = path.relative(process.cwd(), raw)
+        return relative && !relative.startsWith("..") ? relative : raw
+      })()
+    : fallback
+
+  const quotedPath = displayPath.includes(" ")
+    ? `"${displayPath.replace(/"/g, '\\"')}"`
+    : displayPath
+
+  return `npx -y bun ${quotedPath}`
+}
+
+function printUsage(exitCode: number): never {
+  const cmd = formatScriptCommand("scripts/main.ts")
+  console.log(`Baoyu Translate CLI
+
+Usage:
+  ${cmd} <file> [--max-words 5000] [--output-dir <dir>]
+  ${cmd} chunk <file> [--max-words 5000] [--output-dir <dir>]
+
+Commands:
+  chunk              Split markdown into chunks
+
+Options:
+  --max-words <n>    Maximum words per chunk (default: 5000)
+  --output-dir <dir> Write chunks into <dir>/chunks/
+  -h, --help         Show help
+`)
+  process.exit(exitCode)
+}
+
+const args = process.argv.slice(2)
+
+if (args.length === 0) {
+  printUsage(1)
+}
+
+if (args[0] === "-h" || args[0] === "--help") {
+  printUsage(0)
+}
+
+if (args[0] === "chunk") {
+  process.exit(runChunkCli(args.slice(1), `${formatScriptCommand("scripts/main.ts")} chunk`))
+}
+
+process.exit(runChunkCli(args, formatScriptCommand("scripts/main.ts")))