fix(opencode): use canonical GitHub action share links

[cuevaio]

Issue for this PR

Closes #26417

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

GitHub action bot comments were building opencode session links from the session id as https://opencode.ai/s/<id>. That route now returns 404.

This changes the active opencode github run path to use the canonical URL returned by the share service, such as https://opncd.ai/share/<id>, for the footer link and duplicate-share detection. The legacy github/index.ts action entrypoint is updated the same way for consistency. The social-card image still uses the share id, derived from the canonical share URL.

This works because the share API is already the source of truth for the public URL format. The GitHub action no longer guesses the host or route.

How did you verify your code works?

• bun test test/cli/github-action.test.ts test/cli/import.test.ts test/share/share-next.test.ts
• bun typecheck
• pre-push hook: bun turbo typecheck

Screenshots / recordings

N/A, this is not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found

PR #26431: fix(github): use canonical share URL from API instead of constructing it
#26431

Why it's related: This PR appears to address the same issue - using canonical share URLs from the API instead of constructing them manually. Both PRs are fixing the problem where GitHub action links were being built incorrectly and need to use the proper canonical URL format from the share service (e.g., https://opncd.ai/share/<id>). These may be duplicate fixes for the same underlying issue, or PR #26431 might be the related/parent fix that addresses the root cause.