test: Playwright e2e suite (auth, chat, projects, tabular reviews, workflows)

Port of the amal66/mike fork's Playwright end-to-end suite onto the
upstream backend/ + frontend/ layout:

- e2e/: auth.setup (bootstraps a confirmed e2e@mike.local user via the
  Supabase admin API and saves storageState), auth-flows, critical-path
  (create project -> upload PDF -> ask a question -> streamed response),
  chat-management, project-management, tabular-reviews,
  workflows-account; fixtures/test.pdf
- playwright.config.ts: single-worker (shared test user), setup project
  + chromium project with saved auth state; webServer adapted from the
  fork's monorepo command (npm run dev --workspace apps/web) to
  upstream's layouts: backend `npm run dev` (health-checked on :3001)
  and frontend `npm run dev` (:3000)
- root package.json (upstream has none): @playwright/test, typescript
  dev-deps and test:e2e scripts, trimmed from the fork's root manifest
- root tsconfig.json scoped to e2e/ + playwright.config.ts so
  `npx tsc --noEmit` typechecks the suite
- .gitignore: playwright artifacts + e2e/.auth (session tokens)

Specs select by ARIA role/name and placeholder text only - no
data-testid attributes, so no app-code changes are required.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CEguyEgXa9JjCciXCcVemC