Add ticket tribe notification link

[caydyan]

Summary

Addresses stakwork/sphinx-relay#429 by adding the requested explanatory tribe notification link below the bounty action buttons when a sponsoring tribe is available.

The link text is:

Interested in seeing more tickets like this? Join the tribe and get notified about new tickets

It reuses the existing tribe redirect handler, so it opens the same sponsoring tribe destination as the current tribe action button.

Validation

• git diff --check
• Added focused coverage in src/bounties/__tests__/BountyModelButtonSet.spec.tsx for rendering and clicking the new link.

Blocked locally:

• npm test -- --runTestsByPath src/bounties/__tests__/BountyModelButtonSet.spec.tsx --runInBand --no-coverage --silent could not run in this fresh checkout because node_modules/.bin/jest was unavailable. Two yarn install --frozen-lockfile --ignore-scripts attempts stalled in repeated package fetch retries, including a retry with --registry https://registry.npmjs.org --network-timeout 600000.

Bounty

Issue title advertises $@50000. If accepted for bounty payout, route BTC/sats to:

bc1qev5ant33v5y89qqjvcf4mh9hlax5svqf5xd7gc

[caydyan]

Follow-up pushed in 7c6c6b33.

This keeps the requested ticket tribe notification link behavior and tightens the edge cases:

• uses one normalized tribe-availability check for the existing tribe button and the new notification link
• treats blank / none tribe values as missing tribes
• adds keyboard activation for the new link
• extends focused test coverage for keyboard activation and missing-tribe cases

Validation:

• git diff --check
• Dependency install still could not complete locally because yarn install --frozen-lockfile --ignore-scripts --registry https://registry.npmjs.org --network-timeout 600000 remained in repeated network retry loops, so I did not fabricate a Jest result.

[caydyan]

Dependency install succeeded on a rerun, so I was able to run the focused local validation for the current head 7c6c6b3.

Validation now passing locally:

• yarn install --frozen-lockfile --ignore-scripts --registry https://registry.npmjs.org --network-timeout 600000 --non-interactive
• REACT_APP_IS_TEST=true NODE_ENV=test ./node_modules/.bin/jest --coverage --maxWorkers 2 --no-cache --transformIgnorePatterns ./svg/ --runTestsByPath src/bounties/tests/BountyModelButtonSet.spec.tsx --no-coverage --silent (1 suite / 6 tests passed)
• git diff --check origin/master...HEAD
• npx prettier --config .prettierrc.json --check src/bounties/BountyModalButtonSet.tsx src/bounties/tests/BountyModelButtonSet.spec.tsx
• npx eslint src/bounties/BountyModalButtonSet.tsx --max-warnings 100

The earlier blocker was dependency installation network retries; no code change was needed for this validation pass.