fix(dev): pin turbopack root and randomize the dev server port

[EliRobinson]

Summary

• Pins turbopack.root in next.config.ts so Next.js stops inferring the workspace root from sibling lockfiles (a stray one in the home dir, or another worktree under .claude/worktrees/*), which fired the "inferred your workspace root" warning on every pnpm dev.
• Drops the dev script's -p flag entirely (next dev --turbopack, no port arg). next dev already reads PORT from the environment natively, so:
  • Plain pnpm dev falls back to Next's own 3000-and-increment behavior.
  • PORT=3010 pnpm dev still forces a specific port.
  • .claude/launch.json's autoPort: true (added here) can assign a genuinely free port itself and hand it in via PORT — this only works when the script doesn't hardcode -p, which the previous -p ${PORT:-3000} did.
• Moves the E2E server off port 3000 too (playwright.config.ts's PORT → 3417). That's a separate next start instance (pnpm test:e2e → pnpm build && pnpm start), unrelated to pnpm dev, but 3000 is the port most likely to already be held by someone's dev server. playwright.config.ts is now the single source for that port — dropped CI's redundant PLAYWRIGHT_BASE_URL override so it can't drift out of sync.

Why not -p 0?

The issue originally proposed next dev --turbopack -p 0 (OS-assigned random port). I tried that first, but it breaks .claude/launch.json's autoPort integration: autoPort works by picking a free port itself and injecting it via the PORT env var when spawning the dev command — a hardcoded -p 0 overrides that and the two disagree about which port the server is actually on. Dropping -p entirely (confirmed next dev reads PORT on its own) is what makes both paths — manual and autoPort-driven — agree.

Test plan

• pnpm type-check, pnpm lint, pnpm format:check, pnpm test (pre-push hook, all green)
• pnpm dev no longer prints the workspace-root inference warning, verified with sibling worktree lockfiles present
• PORT=4321 next dev --turbopack binds to exactly 4321 with no -p flag present, confirming the env-var path autoPort relies on
• PORT=3417 next start binds to exactly 3417 the same way
• pnpm build && pnpm exec playwright test --project=chromium — all 4 E2E specs pass against the server on port 3417

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