fix(tanstackstart-react): Add workerd and worker export conditions (#19461)

## Problem

When deploying a TanStack Start application to Cloudflare Workers,
importing `@sentry/tanstackstart-react` causes a build failure.

The `@cloudflare/vite-plugin` configures resolve conditions as
`["workerd", "worker", "module", "browser"]` for the SSR environment.
Since this package only defines `browser` and `node` conditions, the
resolver falls through to `browser`, which points to `index.client.js`.
TanStack Start's import-protection plugin denies files matching
`**/*.client.*` in the server environment, causing the build to fail.

Related: TanStack/router#6688

## Solution

Add `workerd` and `worker` export conditions to the `.` entry in
`package.json`, pointing to `index.server.js` (the same target as the
`node` condition). This ensures that bundlers targeting Workers runtimes
resolve to the server entry rather than falling through to the `browser`
condition.

Users deploying to Cloudflare Workers will need `nodejs_compat` enabled
in their wrangler configuration for `@sentry/node` to function correctly
at runtime.

A dedicated Cloudflare entrypoint (without `@sentry/node` dependency)
will be addressed in a follow-up PR.

## Changed files

| File | Change |
|---|---|
| `packages/tanstackstart-react/package.json` | Add `workerd` and
`worker` export conditions pointing to `index.server.js` |

Author: smorimoto

packages/tanstackstart-react/package.json

@@ -19,6 +19,14 @@
     "./package.json": "./package.json",
     ".": {
       "types": "./build/types/index.types.d.ts",
+      "workerd": {
+        "import": "./build/esm/index.server.js",
+        "require": "./build/cjs/index.server.js"
+      },
+      "worker": {
+        "import": "./build/esm/index.server.js",
+        "require": "./build/cjs/index.server.js"
+      },
       "browser": {
         "import": "./build/esm/index.client.js",
         "require": "./build/cjs/index.client.js"