fix(data): enforce canonical city slugs

[AyobamiH]

Problem

Closes #160.

City values are documented as lowercase, underscore-separated slugs, but the dataset contained four values outside that shape and one misspelling. The validator did not enforce the convention.

Changes

• Define the canonical city slug pattern in data/places.schema.json.
• Have validate-places.mjs enforce that schema-owned pattern.
• Normalize the Xiamen and New Delhi records and correct the Philadelphia spelling.
• Correct the API documentation example to show the canonical new_delhi slug.

Verification

• npm run validate
• npm run lint
• npm run typecheck
• npm run test:unit (42 files, 377 tests)
• env -u NEXT_PUBLIC_MAPTILER_KEY npm run build (594 pages)
• npx prettier --check data/places.schema.json data/places/library.json data/places/sat_centre.json scripts/validate-places.mjs
• Negative validation probe confirms that an invalid value such as New Delhi is rejected.
• Local route checks:
  • /city/xiamen, /city/new_delhi, and /city/philadelphia return 200.
  • The previous malformed or misspelled routes return 404.

Known upstream check

The new full-repository npm run format:check command currently reports 127 pre-existing files on the unchanged upstream baseline. This PR does not include unrelated repository-wide formatting.

[vercel]

@AyobamiH is attempting to deploy a commit to the studentsuite Team on Vercel.

A member of the Team first needs to authorize it.