feat(scripts): add frontend and status npm shortcuts

[tryingET]

What problem does this solve?

Closes #121. Implements the slim PR requested in #121 (comment) and the more specific scope on #122: build:frontend, dev:frontend, and app:status only.

How does it solve it?

• Two root npm aliases delegate to the existing frontend scripts, forwarding arguments and child exit codes. Existing desktop build and backend dev remain unchanged.
• app:status reads existing system/status and health endpoints, checks state and matching PID, supports JSON and a bounded deadline, and returns nonzero on draining or invalid/unavailable health.
• Status is cross-platform Node code: no /proc, credentials, dotenv, socket, restart endpoint, Electron changes, or alternate authorization mechanism. It reports a backend snapshot, not checkout ownership or frontend readiness.
• Adds documentation and 15 tests to the existing gating backend Vitest suite. Carries forward applicable feat(just): add operator interface and dual-path restart #127 cases: exact delegation once, quoted argv, no wrapper dotenv loading, failure propagation and preservation of existing commands. Justfile-specific compound CI/package/rebuild-restart recipes are deliberately not introduced.

Fresh branch from upstream main 1b1fcc79, not stacked on #122 or #127. No Justfile, Just dependency/CI, restart command, generated assets, lockfile drift or unrelated fixes.

How did you verify it?

Linux, Node 26.9.0. Dependency directories reused from an installed checkout; source and generated build output isolated in a new worktree. Initial unadjusted baseline exposed Node 26 native webstorage interference and a hidden TMPDIR ancestor rejected by portable-bundle tests. Reran before implementation with NODE_OPTIONS=--no-experimental-webstorage and a plain TMPDIR. No tests or source changed to accommodate these environment differences.

Pristine upstream backend: 428 files passed; 6358 passed, 1 skipped
New tests before implementation: 13 failed, 2 passed
  build:frontend/dev:frontend: expected forwarding script, received undefined
  status/help: npm command exited 1 because app:status was absent
New tests after implementation: 15 passed, 0 skipped
Final backend: 429 files passed; 6373 passed, 1 skipped
Frontend baseline AND final: 281 files passed; 4615 assertions passed
  Both runs also report 2 unhandled PopupTutorial teardown errors:
  ReferenceError: window is not defined, useCleanup.js:41
  Frontend suite exit is nonzero; not claimed green.
npm run build:frontend: production build successful (14.60s)
npm run dev:frontend -- --help: reaches Vite 5.4.21
npm --silent run app:status -- --json: running/healthy, matching PID
node scripts/normalize-eol.mjs --check: 0 rewrites
Git whitespace check: pass

Tests execute real npm against disposable recorders and real local HTTP fixtures. They cover GET-only/no credentials, draining, malformed status, PID mismatch, unhealthy response, HTTP errors, redirects, invalid JSON, oversized responses, timeout, rejected options and help. A read-only smoke also queried a running backend successfully; no live restart, renderer reload or deployment performed. Browser suite and native Windows execution were not run locally.

Checklist

• This does not modify auth, sessions, or credential handling
• This is not a fix for a security vulnerability
• npm test passes
• npm --prefix frontend test passes (same two existing teardown errors as pristine main)
• New behaviour has tests, and I watched them fail before the fix
• Docs updated if the surface changed
• Commit subjects are 72 characters or fewer