[BUG] ModuleNotFoundError for bedrock_agentcore.gateway

**Describe the bug**
Module `bedrock_agentcore.gateway` cannot be imported despite bedrock-agentcore package being installed. When trying to import `GatewayClient` from `bedrock_agentcore.gateway`, Python raises `ModuleNotFoundError: No module named 'bedrock_agentcore.gateway'`.

**To Reproduce**
Steps to reproduce the behavior:
1. Install package with `pip install bedrock-agentcore==0.1.7`
2. Run command `python src/agents/semantic_search_agent/semantic_search_agent.py`
3. See error

**Expected behavior**
The import `from bedrock_agentcore.gateway import GatewayClient` should work without errors, allowing access to the GatewayClient class as shown in the documentation examples.

**Error Output**
```
Traceback (most recent call last):
File "/home/mike/gt/gt-agent-core/src/agents/semantic_search_agent/semantic_search_agent.py", line 9, in
from services.semantic_search_service import SemanticSearchService
File "/home/mike/gt/gt-agent-core/src/services/semantic_search_service.py", line 11, in
from integrations.slack_gateway import SlackGateway
File "/home/mike/gt/gt-agent-core/src/integrations/slack_gateway.py", line 9, in
from bedrock_agentcore.gateway import GatewayClient
ModuleNotFoundError: No module named 'bedrock_agentcore.gateway'
```

**Environment:**
- OS: Ubuntu 24.04.3 LTS
- Python version: 3.12.7
- Package version: bedrock-agentcore==0.1.7
- Installation method: pip

**Additional context**
The import statement matches the examples shown in the AgentCore documentation (https://aws.github.io/bedrock-agentcore-starter-toolkit/examples/gateway-integration.md), but the gateway module appears to be missing from the installed package. The package was installed in a virtual environment and other bedrock-agentcore functionality may be working, but specifically the gateway module is not accessible.

Start with src/agents/semantic_search_agent/semantic_search_agent.py and src/integrations/slack_gateway.py, then reproduce the failure using pip install bedrock-agentcore==0.1.7 and the documented import. Compare the installed package contents with the gateway-integration documentation. Done means the documented GatewayClient import works and the semantic search agent starts without this ModuleNotFoundError.

Written by the indexing model from the issue text.