Fix AWS Bedrock small model selection for APAC regions

[Mr-Neutr0n]

Summary

• Synced crossRegionPrefixes in getSmallModel() with getModel() by adding the missing jp., apac., and au. entries
• Added APAC region handling (ap-northeast-1 -> jp., ap-southeast-2/ap-southeast-4 -> au., other ap-* -> apac.) to the region check logic in getSmallModel(), matching the existing behavior in the Bedrock custom loader's getModel

Fixes #12824

Test plan

• Verify small model selection with ap-northeast-1 (Tokyo) region resolves to jp. prefix
• Verify small model selection with ap-southeast-2 (Sydney) region resolves to au. prefix
• Verify small model selection with other APAC regions resolves to apac. prefix
• Verify us and eu region behavior is unchanged
• Verify global. prefix models are still preferred first

[github-actions]

Hey! Your PR title Fix AWS Bedrock small model selection for APAC regions doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

No duplicate PRs found

[rekram1-node]

?? how is that 1 line change relevant at all