feat: add policy links to attestation questions

[coopernetes]

Summary

• Adds optional links: [{text, url}] field to attestation questions for surfacing policy/compliance URLs in the review form
• Links render as always-visible anchors below each question label — no hover required
• Removes tooltip field (was only used as placeholder text on text inputs; superseded by links)
• Non-breaking: existing configs with no links work unchanged

Config shape

attestations:
  - id: appsec-policy
    type: checkbox
    label: "I confirm this change meets our AppSec requirements"
    required: true
    links:
      - text: "AppSec Policy"
        url: "https://wiki.example.com/appsec"
  - id: ospo-license
    type: checkbox
    label: "I confirm this repo complies with our software license policy"
    required: true
    links:
      - text: "OSPO License Policy"
        url: "https://wiki.example.com/ospo/license"
      - text: "Conflict of Interest Guide"
        url: "https://wiki.example.com/ospo/coi"

Test plan

• ./gradlew build passes
• Links render below question labels in the push review form
• Existing attestation configs with no links field load without errors

closes #366