Update OpenAPI 3.1 documentation links

[popsiclelmlm]

Summary

• Update the starter's OpenAPI Specification links from 3.0.2 to 3.1.0.
• Update component README anchors to the OpenAPI 3.1.0 heading format.

Reproduction

• The starter uses openapi: 3.1.0 in openapi/openapi.yaml.
• Before this change, the description and component docs still linked to OpenAPI 3.0.2 documentation.

Root cause

• The starter spec was upgraded to OpenAPI 3.1.0, but a few documentation links and one paths README reference still pointed at 3.0.2.

Changes

• Point openapi/openapi.yaml to the OpenAPI 3.1.0 spec document.
• Point reusable component object links to OpenAPI 3.1.0 anchors.
• Update the paths README wording from OpenAPI Specification 3.0.2 to 3.1.0.

Tests

• npm test
• git diff --check
• Verified the referenced OpenAPI 3.1.0 headings exist in versions/3.1.0.md.

Screenshots/Logs

• redocly lint validates openapi/openapi.yaml successfully.
• Local Node emitted an engine warning because this machine has Node v22.2.0 and @redocly/cli@2.31.4 expects >=22.12.0 || >=20.19.0 <21.0.0, but lint still completed successfully.

Fixes #116