fix(vite): dedupe shared deps to avoid duplicate React from dashgui

dashgui is a local symlinked package with its own nested node_modules
containing a second copy of react/@mui/@emotion. Vite bundled that nested
React into a dep chunk, causing 'Cannot read properties of null (reading
'useContext')' on routes rendering dashgui/MUI components. Dedupe forces
these shared packages to resolve from dashfront's single tree.

vite.config.js

@@ -62,6 +62,29 @@ function hasRequestBody(method) {
   return method === 'POST' || method === 'PUT' || method === 'PATCH';
 }
 
+// dashgui is a local (symlinked) package with its own nested node_modules.
+// Its nested react/@mui/@emotion copies would otherwise get bundled in,
+// producing a duplicate React instance and "Cannot read properties of null
+// (reading 'useContext')" at runtime. Dedupe forces these to resolve from
+// dashfront's tree. (dashgui's own package.json "exports" map already points
+// the dashgui/* subpaths at its src/, so no alias is needed.)
+const sharedDeps = [
+  'react',
+  'react-dom',
+  'react/jsx-runtime',
+  'react/jsx-dev-runtime',
+  'react-router',
+  'react-router-dom',
+  '@emotion/react',
+  '@emotion/styled',
+  '@mui/material',
+  '@mui/icons-material',
+];
+
+const sharedResolve = {
+  dedupe: sharedDeps,
+};
+
 const sharedServer = {
   // HTTP :4209 — HTTPS :4308 (self-signed; see npm run cert / dev:https)
   port: useHttps ? 4308 : 4209,
@@ -127,6 +150,7 @@ const sharedServer = {
 };
 
 export default defineConfig(({ command }) => ({
+  resolve: sharedResolve,
   build: {
     rolldownOptions: {
       output: {