Fix ~/database/context resolving to browser stub during dev SSR (#12)

`resolve.alias` with `isSsrBuild` only works at build time — during
`npm run dev`, `isSsrBuild` is always false, so `ssrLoadModule` was
loading the browser stub (DatabaseContext = null) instead of the real
AsyncLocalStorage implementation, causing a TypeError on every request.

Replace the alias with an `enforce: 'pre'` plugin that checks
`options.ssr` at resolve time, which Vite correctly sets for both dev
SSR module loading and production SSR builds.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

vite.config.ts

@@ -15,20 +15,22 @@ export default defineConfig(({ isSsrBuild }) => ({
         }
       : undefined,
   },
-  resolve: {
-    alias: isSsrBuild
-      ? []
-      : [
-          {
-            find: "~/database/context",
-            replacement: path.resolve(
-              __dirname,
-              "database/context.browser-stub.ts"
-            ),
-          },
-        ],
-  },
-  plugins: [tailwindcss(), reactRouter(), tsconfigPaths()],
+  plugins: [
+    {
+      name: "database-context-alias",
+      enforce: "pre" as const,
+      resolveId(id, _importer, options) {
+        if (id === "~/database/context") {
+          return options?.ssr
+            ? path.resolve(__dirname, "database/context.ts")
+            : path.resolve(__dirname, "database/context.browser-stub.ts");
+        }
+      },
+    },
+    tailwindcss(),
+    reactRouter(),
+    tsconfigPaths(),
+  ],
   server: {
     allowedHosts: true,
   },