Correct the Next.js document language and Stage-0 metadata

## Context

The root Next.js layout currently declares `lang="zh-Hant"` even though the interface content is primarily English. Its metadata also describes “job creation,” while the current Stage-0 interface explicitly presents job creation as unavailable.

Correct language metadata helps assistive technology, browsers, search previews, and portfolio reviewers understand the interface accurately.

## Newcomer snapshot

- **Difficulty:** Beginner
- **Scope:** Small
- **Primary area:** TypeScript / Next.js metadata and Vitest regression assertions
- **Likely files:** `app/layout.tsx` and `components/network/Phase2O04NetworkShell.test.ts`
- **Python required:** Yes
- **Node/npm required:** Yes
- **Physical hardware required:** No
- **Live device access required:** No
- **Credentials required:** No
- **External API/provider required:** No
- **Task-time network access required:** No, after local dependencies are installed
- **Start with:** `npm run test:unit -- components/network/Phase2O04NetworkShell.test.ts`
- **Before completion:** run the issue's full validation sequence, including typecheck, lint, build, full pytest, and `report-index`
- **Do not change:** routes, controls, provider access, job creation, command execution, network access, or live-device behavior

Dependency installation may require internet access; the access fields above describe the task after local prerequisites are installed.

## Scope

Update only the root document language and public metadata in `app/layout.tsx`, then add focused regression assertions to the existing network-shell test.

Do not add routes, controls, provider access, job creation, or execution behavior.

## Acceptance criteria

- [ ] The root `` element declares the language used by the current interface.
- [ ] The metadata description accurately identifies the Next.js application as a secondary Stage-0 evidence/demo surface.
- [ ] The metadata no longer implies that job creation is currently available.
- [ ] `components/network/Phase2O04NetworkShell.test.ts` protects the corrected language and metadata.
- [ ] Existing routes and Stage-0 safety wording remain unchanged.
- [ ] No provider, API, model, job-creation, command, or live-device behavior is introduced.

## Suggested starting points

- `app/layout.tsx`
- `components/network/Phase2O04NetworkShell.test.ts`
- `app/network/layout.tsx` for the existing secondary-interface wording

## Validation

Run:

- `npm run test:unit -- components/network/Phase2O04NetworkShell.test.ts`
- `npm run typecheck`
- `npm run lint`
- `npm run build`
- `python -m pytest`
- `python network_lab.py --task report-index`

## Safety boundary

This is presentation metadata only. It must not add provider access, submission controls, job creation, command execution, network access, or live-device capability.

Start with app/layout.tsx and compare its public metadata with the wording in app/network/layout.tsx. Run npm run test:unit -- components/network/Phase2O04NetworkShell.test.ts, then add focused assertions in that test for the root language and corrected metadata. Done means the listed typecheck, lint, build, pytest, and report-index validations pass without changing routes or behavior.

Written by the indexing model from the issue text.