feat(mcp-server): canvas shell bundled from the web app's canvas with esbuild

The shell (packages/mcp-server/shell) renders DrawioFrame inside the
shared providers without the chat: its config comes from
window.__MCP_CONFIG__, the four dictionaries ship in the bundle, the
theme is kept under an mcp: localStorage key, and system fonts stand in
for the web fonts. scripts/build-shell.mjs bundles it into dist/shell
with the root's esbuild and Tailwind; check-package caps shell.js at
1.5 MB and shell.css at 300 KB.

packages/mcp-server/shell/dictionary.ts

@@ -0,0 +1,46 @@
+import { i18n, type Locale } from "@/lib/i18n/config"
+import type { Dictionary } from "@/lib/i18n/dictionaries"
+import en from "@/lib/i18n/dictionaries/en.json"
+import ja from "@/lib/i18n/dictionaries/ja.json"
+import zh from "@/lib/i18n/dictionaries/zh.json"
+import zhHant from "@/lib/i18n/dictionaries/zh-Hant.json"
+
+// The web app loads one dictionary on the server (lib/i18n/dictionaries.ts
+// is server-only); the shell ships all four and picks in the browser
+const DICTIONARIES: Record<Locale, Dictionary> = {
+    en,
+    zh,
+    ja,
+    "zh-Hant": zhHant,
+}
+
+/** Our locale for a language tag ("zh-TW", "ja-JP", "en-US"), or null */
+export function matchLocale(tag: string): Locale | null {
+    const lower = tag.trim().toLowerCase()
+    if (!lower) return null
+    if (/^zh-(hant|tw|hk|mo)\b/.test(lower)) return "zh-Hant"
+    const base = lower.split("-")[0]
+    if (base === "zh") return "zh"
+    if (base === "ja") return "ja"
+    if (base === "en") return "en"
+    return null
+}
+
+/**
+ * The shell's language: the server's DRAWIO_LANG when it is one of ours,
+ * else the browser's first language we have, else English.
+ */
+export function pickLocale(
+    configLang: string,
+    browserLangs: readonly string[],
+): Locale {
+    for (const tag of [configLang, ...browserLangs]) {
+        const locale = matchLocale(tag)
+        if (locale) return locale
+    }
+    return i18n.defaultLocale
+}
+
+export function getShellDictionary(locale: Locale): Dictionary {
+    return DICTIONARIES[locale]
+}