fix(electron-compat): prepend globalThis.Bun shim to prevent Electron/Node crash

On Node/Electron, globalThis.Bun is undefined. The Bun bundler emits top-level
  var { spawn } = globalThis.Bun;
destructures from its internal modules, causing 'Cannot destructure property
of undefined' before any plugin hook is reached (25 occurrences in dist/index.js).

Fix:
- Add src/electron-compat.ts: a side-effect module that populates globalThis.Bun
  with node:child_process-backed spawn/spawnSync shims when Bun is unavailable
- Add script/prepend-electron-shim.ts: post-build script that prepends the shim
  code to dist/index.js, guaranteeing it runs BEFORE the top-level destructures
  (Bun bundler does not preserve import side-effect evaluation order reliably)
- Update build script to run prepend-shim after bundling
- Add src/electron-compat.test.ts verifying shim position in dist

The shim only activates when globalThis.Bun is absent (real Bun runtime is
unaffected). Spawn-dependent features degrade gracefully at call time.

Fixes #3797 (follow-up to #3795/#3796)

package.json

@@ -22,7 +22,8 @@
     "./schema.json": "./dist/oh-my-opencode.schema.json"
   },
   "scripts": {
-    "build": "bun build src/index.ts --outdir dist --target bun --format esm --external @ast-grep/napi --external zod && tsc --emitDeclarationOnly && bun build src/cli/index.ts --outdir dist/cli --target bun --format esm --external @ast-grep/napi && bun run build:schema",
+    "build": "bun build src/index.ts --outdir dist --target bun --format esm --external @ast-grep/napi --external zod && bun run build:prepend-shim && tsc --emitDeclarationOnly && bun build src/cli/index.ts --outdir dist/cli --target bun --format esm --external @ast-grep/napi && bun run build:schema",
+    "build:prepend-shim": "bun run script/prepend-electron-shim.ts",
     "build:all": "bun run build && bun run build:binaries",
     "build:binaries": "bun run script/build-binaries.ts",
     "build:schema": "bun run script/build-schema.ts",