Add one-command live and mocked development modes

[itsjling]

Closes #25

Summary:

• add supervised live and mock development commands with safe port selection and clean signal handling
• serve live JSON and SSE through Vite without a production build
• keep each mock stage visible until the browser reads it, then show progress, failure, retry, and completion

Stack:

• based on PR Make the fresh-checkout demo self-contained #42 / issue Make demo development work in every fresh checkout #24

Verification:

• npm run lint
• npm test (72 passed)
• npm run docs:check
• npm run docs:build
• Fallow changed-code audit against codex/issue-024-fresh-demo

Stack

1. Keep live refresh ordered and fault-tolerant #61
2. Make the fresh-checkout demo self-contained #42
3. Add one-command live and mocked development modes #58 👈 current
4. Prove one full review journey in a real browser #59

[chatgpt-codex-connector]

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Reviewed commit: a905ad4d6d

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[itsjling]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: f95f80b726

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".