fix: support Node runtime in OpenCode Desktop

[yikZero]

Problem

OpenCode Desktop runs plugin hooks in its Electron/Node backend. The current proxy assumes a Bun host at module load and startup (import.meta.dir, Bun.serve, and Bun.spawn). In Desktop, the config hook fails before it can seed the discovered model catalog, so the configured cursor provider is omitted from the provider list.

Fix

• add a small runtime adapter that keeps the existing Bun server/process path and provides a Node HTTP server fallback
• launch HTTP/2 bridge scripts with the current Node/Electron executable, using ELECTRON_RUN_AS_NODE for Electron
• resolve bundled bridge paths with standard import.meta.url
• add a Node regression that covers proxy requests and a real HTTP/2 child-process round trip
• document OpenCode Desktop / Node runtime support

Verification

• bun run build
• bun run test:node
• package dry run includes dist/runtime.js and both HTTP/2 bridge scripts
• OpenCode CLI 1.18.19: live Cursor catalog loaded and cursor/default returned FORK_CLI_OK
• OpenCode Desktop 1.18.23: embedded Electron/Node server reported Cursor connected with 92 model entries; a Desktop request using providerID: cursor / modelID: default returned DESKTOP_FORK_OK

bun run test currently reaches the existing testCursorVariantHooks assertion and fails with Expected runtime provider to expose one GPT family. The same failure reproduces on an untouched worktree at upstream commit ef37212, before this patch is applied; the runtime-specific Node regression passes.