Add AWS Bedrock builders (Agent, Knowledge Base, Data Source, Guardrail)

[Thorium]

Summary

• Adds src/Bedrock.fs with 4 computation expression builders: bedrockAgent, bedrockKnowledgeBase, bedrockDataSource, bedrockGuardrail
• Integrates into Stack.fs with Operation DU cases, processOperation, Yield, and Bind methods for let! support
• Adds 35 Expecto tests covering required field validation, property assignment, tags, and mutable resource references

Details

All builders follow the established Config/Spec/Builder pattern:

• BedrockAgentBuilder — wraps CfnAgent with foundation model, instruction, auto-prepare defaults
• BedrockKnowledgeBaseBuilder — wraps CfnKnowledgeBase with typed IKnowledgeBaseConfigurationProperty and IStorageConfigurationProperty parameters
• BedrockDataSourceBuilder — wraps CfnDataSource with typed IDataSourceConfigurationProperty, encryption, and vector ingestion config
• BedrockGuardrailBuilder — wraps CfnGuardrail with typed policy config interfaces (content, grounding, PII, topic, word) and ICfnTag conversion

Conventions followed:

• Typed CDK interface parameters (not obj) for type-safe custom operations
• Guarded tag Combine pattern (matching AppRunner/XRay)
• Inline Yield/Zero defaults, state2.XxxName in Combine
• CfnTag conversion from (string * string) list in Run
• Documentation script (docs/bedrock.fsx) and docs/index.fsx updated

Build & Tests

• Build: 0 warnings, 0 errors
• Tests: 393 passed, 3 skipped (pre-existing RDS/XRay), 0 failures