fix: support AWS GovCloud and China region ARNs in Bedrock validation

[roomote]

Description

This PR attempts to address Issue #9481 by adding support for AWS GovCloud and China region ARNs in the Bedrock validation logic. Feedback and guidance are welcome.

Problem

The ARN validation regex was too strict and only accepted standard AWS partition ARNs (arn:aws:...) but rejected valid GovCloud (arn:aws-us-gov:...) and China region (arn:aws-cn:...) ARNs.

Solution

• Updated the ARN validation regex in both validateBedrockArn and parseArn functions to accept aws, aws-us-gov, and aws-cn partitions
• Added comprehensive test coverage for GovCloud and China region ARNs

Changes

• Updated ARN regex in webview-ui/src/utils/validate.ts to support aws-us-gov and aws-cn partitions
• Updated ARN regex in src/api/providers/bedrock.ts parseArn method to support GovCloud and China regions
• Added new test file validateBedrockArn.spec.ts with tests for all partition types
• Added tests in bedrock.spec.ts for GovCloud and China ARN parsing

Testing

• ✅ All new tests for GovCloud and China ARN validation pass
• ✅ All existing Bedrock provider tests pass
• ✅ Type checking passes
• ✅ Linting passes

Example ARNs now supported

• GovCloud: arn:aws-us-gov:bedrock:us-gov-west-1:123456789012:inference-profile/us-gov.anthropic.claude-sonnet-4-5-20250929-v1:0
• China: arn:aws-cn:bedrock:cn-north-1:123456789012:foundation-model/anthropic.claude-v2

Fixes #9481

[roomote]

Rooviewer   See task on Roo Cloud

Review complete. No issues found.

The implementation correctly adds support for AWS GovCloud (aws-us-gov) and China (aws-cn) region ARNs. The changes are minimal, well-tested, and backwards compatible.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[wisestmumbler]

Any updates for this one?