refactor: rename directories for clarity (agent_patterns, agentcore_gateway, agentcore_tools)

[razkenari]

Naming improvements to make the repo structure clearer.

1. patterns/ → agent_patterns/: Renaming to agent_patterns/ makes it immediately clear that this is where agent code lives.
2. gateway/ → agentcore_gateway/ and tools/ → agentcore_tools/: Prefixing with agentcore_ makes it clear these are AgentCore-specific features, not general-purpose utilities.

Files to update: All references to the old paths in: infra-cdk/, infra-terraform/, docs/, scripts/, test-scripts/, Makefile, pyproject.toml, .dockerignore, docker/, config.yaml.