feat(browser-agent): Improve activity polling error diagnostics and add modular deployment

## Activity Poller Error Logging Improvements
- Extract and display detailed AWS error codes and messages
- Add automatic troubleshooting hints for common errors:
  - AccessDenied/Permission errors
  - InvalidArn/Activity not found
  - Network/timeout errors
  - Credential errors
- Show configuration details at startup (ARN, profile, worker name)
- Add context logging (Activity ARN, AWS Profile) on failures

## Template Tab Fix
- Add template_config field to BaseAgentConstruct
- Enable Template tab display in agent details modal
- Fix missing template configuration storage in DynamoDB

## BT Wholesale Agent Deployment
- Add BroadbandAvailabilityBtWholesaleStack to app.py deployment
- Configure dependencies on SharedLLMStack, AgentRegistry, SharedInfrastructure
- Wire browser_remote tool with template support

## Testing & Documentation
- Add test_activity_connection.rs example for quick connectivity testing
- Create MODULAR_DEPLOYMENT_DESIGN.md for future configuration-based deployment

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: guyernest

app.py

@@ -55,6 +55,7 @@
 from stacks.agents.browser_automation_agent_unified_llm_stack import BrowserAutomationAgentUnifiedLLMStack
 from stacks.agents.broadband_agent_unified_llm_stack import BroadbandAgentUnifiedLLMStack
 from stacks.agents.broadband_checker_structured_stack import BroadbandCheckerStructuredStack
+from stacks.agents.broadband_availability_bt_wholesale_stack import BroadbandAvailabilityBtWholesaleStack
 from stacks.agents.travel_time_checker_structured_stack import TravelTimeCheckerStructuredStack
 from stacks.agents.browser_automation_structured_stack import BrowserAutomationStructuredStack
 from stacks.shared.structured_output_infrastructure_stack import StructuredOutputInfrastructureStack
@@ -456,6 +457,19 @@ def main():
     broadband_checker.add_dependency(shared_infrastructure_stack)  # For ToolRegistry
     broadband_checker.add_dependency(agentcore_browser_tools)  # For browser tool
 
+    # BT Wholesale Broadband Availability Agent - Schema-driven with template support
+    bt_wholesale_agent = BroadbandAvailabilityBtWholesaleStack(
+        app,
+        f"BroadbandAvailabilityBtWholesaleStack-{environment}",
+        env_name=environment,
+        env=env,
+        description=f"Schema-driven BT Wholesale broadband availability checker with template support for {environment} environment"
+    )
+    bt_wholesale_agent.add_dependency(shared_llm_stack)
+    bt_wholesale_agent.add_dependency(agent_registry_stack)
+    bt_wholesale_agent.add_dependency(shared_infrastructure_stack)  # For TemplateRegistry and ToolRegistry
+    bt_wholesale_agent.add_dependency(browser_remote_tool)  # For browser_remote tool
+
     # Travel Time Checker with Structured Output - using unified LLM generator pattern
     travel_time_checker = TravelTimeCheckerStructuredStack(
         app,