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/server/src/index.ts

@@ -29,13 +29,14 @@ import { SideCarManager } from "./sidecars/manager"
 import { ClientConnectionManager } from "./clients/connection-manager"
 import { PluginChannelManager } from "./plugins/channel"
 import { VoiceModeManager } from "./plugins/voice-mode"
+import { readServerPackageVersion, resolveServerPublicDir } from "./runtime-paths"
 
 const require = createRequire(import.meta.url)
 
-const packageJson = require("../package.json") as { version: string }
+const packageJson = { version: readServerPackageVersion(import.meta.url) }
 const __filename = fileURLToPath(import.meta.url)
 const __dirname = path.dirname(__filename)
-const DEFAULT_UI_STATIC_DIR = path.resolve(__dirname, "../public")
+const DEFAULT_UI_STATIC_DIR = resolveServerPublicDir(import.meta.url)
 
 interface CliOptions {
   host: string