Model dropdown hardcodes us. region prefix and ignores Bedrock region configuration

Description:

When using Claude Code with AWS Bedrock in non-US regions (e.g., \ap-south-1\), the model switcher dropdown has several issues that make it unusable:

Issues:

1. Hardcoded region prefix: When selecting a model from the dropdown (e.g., \"Opus 4.5\"), the extension writes \us.anthropic.claude-opus-4-5-20251101-v1:0\ to \claudeCode.selectedModel\, regardless of the configured AWS region. This causes API errors when using non-US regions that require \global.\ prefix.

1. Incorrect UI display: The dropdown shows \"Default (currently Sonnet 4.5)\" even when \global.anthropic.claude-opus-4-5-20251101-v1:0\ is configured in settings.

1. Ignores environment variables: The \ANTHROPIC_MODEL\ environment variable is set to Opus, but \"Default (recommended)\" still uses Sonnet.

Environment:

\\\json
{
"claudeCode.selectedModel": "global.anthropic.claude-opus-4-5-20251101-v1:0",
"claudeCode.environmentVariables": [
{
"name": "CLAUDE_CODE_USE_BEDROCK",
"value": "1"
},
{
"name": "AWS_REGION",
"value": "ap-south-1"
},
{
"name": "ANTHROPIC_MODEL",
"value": "arn:aws:bedrock:ap-south-1:588625695333:inference-profile/global.anthropic.claude-opus-4-5-20251101-v1:0"
}
]
}
\\\

Steps to Reproduce:

1. Configure Claude Code to use AWS Bedrock in \ap-south-1\ region
2. Set \claudeCode.selectedModel\ to \global.anthropic.claude-opus-4-5-20251101-v1:0\
3. Click on the model dropdown and select \"Opus 4.5\"
4. Settings are changed to \us.anthropic.claude-opus-4-5-20251101-v1:0\
5. API error occurs: \"400 The provided model identifier is invalid\"

Expected Behavior:

• Extension should detect the configured AWS region and use the appropriate inference profile prefix (\global.\ for cross-region profiles, \us.\ for US regions)
• Or, provide a setting to configure the region prefix
• Or, read from environment variables to determine the correct model identifier
• UI should accurately display which model is currently selected

Workaround:

Manually edit \settings.json\ and avoid using the dropdown entirely. This is tedious and defeats the purpose of having a UI.

Impact:

This makes Claude Code unusable for Bedrock users in non-US regions who need to switch models frequently.