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

.gitignore

@@ -0,0 +1,18 @@
+# dependencies
+node_modules/
+
+# build output
+dist/
+public/*.js
+public/*.js.map
+
+# local Claude Code settings (not shared)
+.claude/settings.local.json
+
+# logs / OS cruft
+*.log
+npm-debug.log*
+.DS_Store
+
+# test coverage
+coverage/