[TASK] dotAI: LangChain4J - Amazon Bedrock provider

[fmontes]

Description

Add AWS Bedrock as a supported provider in the dotAI LangChain4J integration layer. Bedrock is a managed platform that proxies multiple model families (Anthropic, Amazon Titan, Cohere, Meta, etc.) via a unified Converse API — a single integration covers all of them.

This builds on the LangChain4J abstraction established in #35183 (Phase 1 — OpenAI).

Implementation outline:

• Add langchain4j-bedrock dependency
• Add bedrock case to LangChain4jModelFactory switch
• Implement buildBedrockChatModel using BedrockRuntimeClient with explicit or IAM role credentials
• Implement buildBedrockEmbeddingModel with automatic Titan/Cohere dispatch by model ID prefix
• Add embeddingInputType field to ProviderConfig (Cohere-specific; default: search_document)
• buildBedrockImageModel throws UnsupportedOperationException (no LangChain4J support)

Acceptance Criteria

• bedrock is selectable as a provider in providerConfig for chat and embeddings sections
• When accessKeyId / secretAccessKey are omitted, credentials resolve via DefaultCredentialsProvider (IAM role, environment, ~/.aws/credentials)
• Embedding dispatch routes cohere.* model IDs to BedrockCohereEmbeddingModel and all others to BedrockTitanEmbeddingModel
• embeddingInputType is honored for Cohere; silently ignored for Titan
• Image generation throws UnsupportedOperationException with a clear message
• Unit tests cover Bedrock chat and embedding builders (Titan + Cohere) in LangChain4jModelFactoryTest

Additional Context

• Parent: [FEATURE] dotAI: LangChain4J integration — Phase 1 (OpenAI) #35183 (Phase 1 - OpenAI)
• Epic: EPIC: dotAI Multi-Provider Support #33970 (dotAI Multi-Provider Support)
• Implementation PR: feat(dotAI): Dot AI LangChain4J - Amazon Bedrock #35242

Sample configuration:

{
  "chat": {
    "provider": "bedrock",
    "region": "us-east-1",
    "model": "anthropic.claude-3-5-sonnet-20241022-v2:0",
    "maxTokens": 16384
  },
  "embeddings": {
    "provider": "bedrock",
    "region": "us-east-1",
    "model": "amazon.titan-embed-text-v2:0"
  }
}