Hide non-functional Bedrock provider from UI and README

[0xMMA]

Context

AWS Bedrock is listed as a supported provider in the README and available in the settings dropdown, but it is not implemented.

Problem

Selecting Bedrock as provider and attempting to enhance text returns:

AWS Bedrock is not yet supported. Please select a different provider

(internal/features/enhance/service.go:88-89)

Despite this, Bedrock appears as a working option:

• Provider dropdown in frontend/src/app/features/settings/settings.component.ts:401
• API key field (providerKeys) at line 430
• README.md lists "AWS Bedrock (Claude, Titan, etc.)" as supported

Acceptance Criteria

• Bedrock removed from provider dropdown and key fields until implemented
• README updated to note Bedrock is not yet available
• CLAUDE.md description updated to remove Bedrock from the provider list