fix(plugins): install local plugins on packaged desktop

The plugin compiler spawned esbuild through app.asar, and the subprocess
imported the React client barrel. Point esbuild at the unpacked binary,
add a react-free @paseo/plugin/server entry, and pass a typed PluginTheme
so plugin UI follows the active theme on desktop and mobile.

plugin-examples/linear/issues.server.ts

@@ -1,4 +1,4 @@
-import type { PluginAttachmentSearchPayload } from "@paseo/plugin";
+import type { PluginAttachmentSearchPayload } from "@paseo/plugin/server";
 import type { output as ZodOutput } from "zod";
 import { searchIssuesRpc } from "./issues.shared";
 import { createLinearIssueSearch } from "./linear";