fix(social-codenewbie): tolerate invalid article timestamps

[aiirvizionz]

Summary

• avoid throwing after successful CodeNewbie article creation when published_at or created_at is malformed
• fall back to the current timestamp for publishedAt
• add focused regression coverage for invalid CodeNewbie article timestamps

Tests

• vitest run packages/social/codenewbie/src/index.test.ts
• tsc -p packages/social/codenewbie/tsconfig.json --noEmit

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.

[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.