fix(config): prepend bun export condition under bun runtime

When running the dev server under `bun --bun`, `_resolveExportConditions`
only pushed "node" to Vite's resolve conditions. This caused Vite's
ModuleRunner to load srvx's and h3's Node adapters inside the dev worker,
returning a srvx `NodeResponse` to `Bun.serve` — which Bun rejects, falling
back to its default response and breaking every `/_nitro/*` request with a
Parse Error.

Detect Bun via `"Bun" in globalThis` (matching the existing pattern in
`src/presets/vercel/utils.ts`) and prepend "bun" so it wins for packages
declaring both conditions, while keeping "node" for packages that only
declare "node". Pure Node setups are unchanged.

Closes #4228

Author: sotasan

src/config/resolvers/export-conditions.ts

@@ -21,6 +21,9 @@ function _resolveExportConditions(
   }
 
   if (opts.node) {
+    if ("Bun" in globalThis) {
+      conditions.push("bun");
+    }
     conditions.push("node");
   }