[codex] add web app manifest id

[Sean-Kenneth-Doherty]

Summary

• add a stable root-relative id to the web app manifest
• keep it aligned with the existing root start_url and scope
• make the manifest identity explicit for browsers and app catalog tooling

Addresses #347

Validation

• git diff --check
• parsed public/manifest.json and confirmed id, start_url, and scope are all /
• GITHUB_TOKEN=$(gh auth token) pnpm build
• parsed generated dist/manifest.json and confirmed id, start_url, and scope are all /

Reference

MDN documents the manifest id member as the unique identifier for a web app and recommends using a leading / for a root-relative identifier: https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/Manifest/Reference/id

[Sean-Kenneth-Doherty]

Validation notes for this manifest best-practices slice:

• git diff --check passes
• parsed public/manifest.json and confirmed id, start_url, and scope are all /
• GITHUB_TOKEN=$(gh auth token) pnpm build passes
• parsed generated dist/manifest.json and confirmed id, start_url, and scope are all /

Reference: MDN documents the web app manifest id as the unique identifier for the app and recommends a leading / for a root-relative identifier: https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/Manifest/Reference/id