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/theme.ts

@@ -0,0 +1,61 @@
+import { useSettingsStore } from "@/stores/settings-store"
+import type { ShellConfig } from "./runtime-config"
+
+/**
+ * localStorage key of the user's theme choice here: "true" dark, "false"
+ * light, none: the server's DRAWIO_DARK, else the system. Its own prefix,
+ * so a web app dev server on the same port keeps its own settings.
+ * index.html repeats the key in its inline script (run before this bundle).
+ */
+export const THEME_STORAGE_KEY = "mcp:dark-mode"
+
+/** Whether the shell is dark, from the choice stored here, the server's
+ * setting and the system */
+export function isDarkPreferred(
+    stored: string | null,
+    drawioDark: ShellConfig["drawioDark"],
+    systemDark: boolean,
+): boolean {
+    if (stored === "true" || stored === "false") return stored === "true"
+    if (drawioDark === "auto") return systemDark
+    return drawioDark === "dark"
+}
+
+function read(): string | null {
+    try {
+        return localStorage.getItem(THEME_STORAGE_KEY)
+    } catch {
+        return null
+    }
+}
+
+// The canvas components read the settings store's isDark (and the theme
+// class, set before the first paint by index.html)
+function apply(isDark: boolean) {
+    document.documentElement.classList.toggle("dark", isDark)
+    useSettingsStore.setState({
+        hydrated: true,
+        isDark,
+        theme: isDark ? "dark" : "light",
+    })
+}
+
+/** Take the theme the inline script chose, and follow the system while
+ * nothing else decides */
+export function initTheme(drawioDark: ShellConfig["drawioDark"]) {
+    const query = window.matchMedia("(prefers-color-scheme: dark)")
+    apply(isDarkPreferred(read(), drawioDark, query.matches))
+    query.addEventListener("change", (event) => {
+        apply(isDarkPreferred(read(), drawioDark, event.matches))
+    })
+}
+
+/** The user's choice, kept for the next visit */
+export function setDark(isDark: boolean) {
+    try {
+        localStorage.setItem(THEME_STORAGE_KEY, String(isDark))
+    } catch {
+        // Storage can be unavailable (private mode, quota)
+    }
+    apply(isDark)
+}