Don't depend on Node anymore (#346)

## Summary
- package `packages/server` as a standalone desktop executable so
Electron and Tauri no longer depend on a system-installed Node runtime
in production
- align Electron and Tauri startup logic around launching the packaged
server, resolving binaries from the user shell, and bundling the same
server resources into both desktop apps
- replace the workspace instance proxy path that used
`@fastify/reply-from` with a direct streaming proxy so packaged
standalone builds can talk to spawned `opencode` instances correctly

## Why
Desktop production builds were still depending on a user-provided Node
runtime to launch `packages/server`, which made packaging less
self-contained and created different behavior across machines. While
moving to a standalone server executable, we also found that
Bun-compiled standalone builds could start `opencode` successfully but
failed when proxying requests to those instances through `reply-from`.

The goal of this change is to make desktop production startup
self-contained, keep Electron and Tauri behavior aligned, and restore
correct communication with local `opencode` instances in packaged
builds.

## What Changed
- added a standalone build path for `packages/server` and bundle
`codenomad-server` into desktop resources
- updated Electron production startup to resolve and launch the
standalone server executable
- updated Tauri production startup to resolve and launch the standalone
server executable with matching cwd and shell behavior
- added runtime path helpers so the packaged server can reliably find
its bundled UI, auth templates, config template, and package metadata
- improved bare binary resolution so commands like `opencode` can be
resolved from the user's login shell environment
- upgraded the server stack to newer Fastify-compatible packages needed
for the standalone/runtime work
- replaced the workspace instance proxy implementation with a direct
streaming proxy for requests to spawned `opencode` instances
- updated Electron and Tauri build/prebuild scripts to generate and
package the standalone server, while also repairing missing
platform-specific optional binaries during packaging

## Benefits
- desktop production builds no longer require Node to be installed on
the user's system
- Electron and Tauri now use the same packaged server model in
production, reducing platform drift
- packaged desktop apps can successfully create workspaces, launch
`opencode`, and proxy health/session traffic to those instances
- the server bundle is more self-contained and resilient to different
launch environments
- desktop packaging is more predictable because the required server
executable is built and bundled as part of the app build flow

packages/electron-app/scripts/build.js

@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 
 import { spawn } from "child_process"
-import { existsSync } from "fs"
+import { existsSync, readFileSync } from "fs"
 import path, { join } from "path"
 import { fileURLToPath } from "url"
 
@@ -14,6 +14,46 @@ const npxCmd = process.platform === "win32" ? "npx.cmd" : "npx"
 const nodeModulesPath = join(appDir, "node_modules")
 const workspaceNodeModulesPath = join(workspaceRoot, "node_modules")
 
+function getPlatformEsbuildPackage() {
+  const platformKey = `${process.platform}-${process.arch}`
+  const platformPackages = {
+    "linux-x64": "@esbuild/linux-x64",
+    "linux-arm64": "@esbuild/linux-arm64",
+    "darwin-arm64": "@esbuild/darwin-arm64",
+    "darwin-x64": "@esbuild/darwin-x64",
+    "win32-arm64": "@esbuild/win32-arm64",
+    "win32-x64": "@esbuild/win32-x64",
+  }
+
+  return platformPackages[platformKey] ?? null
+}
+
+async function ensureEsbuildPlatformBinary() {
+  const pkgName = getPlatformEsbuildPackage()
+  if (!pkgName) {
+    return
+  }
+
+  const platformPackagePath = join(workspaceNodeModulesPath, ...pkgName.split("/"))
+  if (existsSync(platformPackagePath)) {
+    return
+  }
+
+  let esbuildVersion = ""
+  try {
+    esbuildVersion = JSON.parse(readFileSync(join(workspaceNodeModulesPath, "esbuild", "package.json"), "utf-8")).version ?? ""
+  } catch {
+    // leave version empty; fallback install will use latest compatible
+  }
+
+  const packageSpec = esbuildVersion ? `${pkgName}@${esbuildVersion}` : pkgName
+  console.log("📦 Step 0/3: Restoring esbuild platform binary...\n")
+  await run(npmCmd, ["install", packageSpec, "--no-save", "--ignore-scripts", "--fund=false", "--audit=false"], {
+    cwd: workspaceRoot,
+    env: { NODE_PATH: workspaceNodeModulesPath },
+  })
+}
+
 const platforms = {
   mac: {
     args: ["--mac", "--x64", "--arm64"],
@@ -105,6 +145,8 @@ async function build(platform) {
   console.log(`\n🔨 Building for: ${config.description}\n`)
 
   try {
+    await ensureEsbuildPlatformBinary()
+
     console.log("📦 Step 1/3: Building CLI dependency...\n")
     await run(npmCmd, ["run", "build", "--workspace", "@neuralnomads/codenomad"], {
       cwd: workspaceRoot,