feat: T1 scaffold — package.json, tsconfig (backend+web), vitest, dirs

- All deps declared once (express5, ws, node-pty, @xterm/xterm6, addon-fit;
  dev: typescript6, tsx, vitest4, @types/node|ws|express)
- postinstall chmod +x node-pty spawn-helper (prebuild ships it non-exec → posix_spawnp fails)
- node-pty verified: require + real PTY spawn (exitCode 0)
- npm test passes with no tests (passWithNoTests)
- tsconfig.web.json type-checks frontend; browser bundling strategy still TBD (see log)

T1 of docs/PLAN.md

tsconfig.web.json

@@ -0,0 +1,17 @@
+{
+  "// note": "Frontend (browser) config for public/*.ts. moduleResolution Bundler lets bare imports (@xterm/xterm) type-check. NOTE: emits nothing — the actual browser bundle strategy (esbuild/import-map/CDN) is unresolved; see T1 log entry. This config currently serves as type-check for the frontend.",
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "types": [],
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "noEmit": true
+  },
+  "include": ["public"]
+}