feat: Electron desktop wrapper — LearnHarness.app (macOS arm64)

The web app becomes a desktop app without changing shape: the Electron
shell spawns the Next standalone server on a loopback port and points a
sandboxed window at it. All app logic stays in the Next server.

Bands:

1. LH_DATA_DIR seam (config.ts): PATHS.data/chats/graph derive from
   process.env.LH_DATA_DIR (else repo data/, unchanged in dev). New
   PATHS.modelCache routes the transformers.js embedding-model cache
   (~300MB) to <data>/models when the seam is set — the default cache
   inside node_modules is read-only in a packaged bundle. All existing
   fs writes flow through PATHS; teacherPrompt stays ROOT-anchored
   (read-only asset, ships inside the bundle by design).
   tests/data-dir-seam.test.ts covers set/unset via child process.

2. Standalone build (next.config.ts + scripts/build-server.mjs):
   output 'standalone'; outputFileTracingExcludes data/**/* keeps the
   repo's real session data out of the bundle (verified: an unexcluded
   scratch build traced 34 files / 716K of real chats + ledgers).
   Two empirically-verified tracer gaps required outputFileTracingIncludes:
   pi-ai's provider catalog (JSON import attributes — 39 files, 500s on
   /api/models without them) and onnxruntime-node's sibling dylib
   (libonnxruntime.dlopen via @rpath). build-server.mjs copies public/
   and .next/static per docs, refuses a leaked data/ dir, and asserts
   the runtime-read prompt .md assets are traced.

3. Electron shell (electron/main.cjs, no preload):
   - single-instance lock (two instances would fight over the data dir);
   - free port via listen(0); spawn via process.execPath +
     ELECTRON_RUN_AS_NODE=1 with PORT/HOSTNAME=127.0.0.1/LH_DATA_DIR;
   - BYOK: userData/auth.json, flat {VAR: value} JSON, mode 0600,
     merged into the child env only when absent from the real env
     (auth UI is the settings milestone; file is hand-editable);
   - poll until the server answers (no ready event), then open a
     contextIsolation+sandbox window; deny-by-default permission
     handler (media allowed only from the loopback origin — mic/STT
     groundwork); will-navigate pinned to origin, window.open denied
     with external links to the system browser; macOS Edit-menu roles;
   - quit path SIGTERM→3s→SIGKILL + exit/SIGHUP nets; child stdout
     mirrored to userData/logs/main.log;
   - dev mode via LH_DEV_URL: no spawn, points at next dev (HMR).

4. Packaging (electron-builder.yml + build/entitlements.mac.plist):
   files = electron shell only; the whole .next payload ships via
   extraResources from .next (filter standalone/**/*) — NOT from
   .next/standalone directly: electron-builder hard-excludes a copy's
   root node_modules and the default pattern is a literal match, so
   node_modules/ and .next/ were silently dropped and the server died
   with 'Cannot find module next'. Asar holds no native code.
   Unsigned (identity: null) until a Developer ID cert exists; hardened
   runtime + audio-input entitlements laid now for the STT milestone.
   desktop:dev / desktop:dist scripts (electron 44, electron-builder 26).

Live smoke of the packaged .app: server up on a random loopback port,
all API routes 200, a real GLM chat turn answered end-to-end via
auth.json BYOK, chat persisted under userData/data, second instance
exited via the lock, no orphaned server child after quit.

Gates: typecheck, eslint, 500/500 tests (+2 data-dir-seam), build.

package.json

@@ -4,13 +4,16 @@
 	"description": "A standalone learning harness: a teacher agent (AI SDK) with quiz/ask interactions, session artifacts, and a derived knowledge graph of what the learner knows.",
 	"type": "module",
 	"private": true,
+	"main": "electron/main.cjs",
 	"scripts": {
 		"dev": "next dev",
 		"build": "next build",
 		"start": "next start",
 		"test": "NODE_ENV=test tsx --test tests/*.test.ts tests/*.test.tsx",
 		"lint": "eslint .",
-		"typecheck": "tsc --noEmit"
+		"typecheck": "tsc --noEmit",
+		"desktop:dev": "concurrently -k \"next dev\" \"LH_DEV_URL=http://localhost:3000 electron .\"",
+		"desktop:dist": "next build && node scripts/build-server.mjs && electron-builder --mac --arm64"
 	},
 	"dependencies": {
 		"@ai-sdk/react": "^4.0.79",
@@ -66,6 +69,9 @@
 		"@types/react-dom": "^19.2.4",
 		"@types/turndown": "^5.0.6",
 		"@typescript-eslint/parser": "^8.68.0",
+		"concurrently": "^10.0.5",
+		"electron": "^44.4.1",
+		"electron-builder": "^26.15.3",
 		"eslint": "^9.39.5",
 		"eslint-import-resolver-typescript": "^4.4.5",
 		"eslint-plugin-import": "^2.32.0",