refactor: extract services layer, Result type, and ErrorCode classification

- Add DI container (src/services/) with AgentExecutionService, ConfigLoaderService, and ExploitationCheckerService — pure domain logic with no Temporal dependencies
- Introduce Result<T, E> type and ErrorCode enum for code-based error classification in classifyErrorForTemporal, replacing scattered string matching
- Consolidate billing/spending cap detection into utils/billing-detection.ts with shared pattern lists across message-handlers, claude-executor, and error-handling
- Extract LogStream abstraction for append-only logging with backpressure, used by both AgentLogger and WorkflowLogger
- Simplify activities.ts from inline lifecycle logic to thin wrappers delegating to services, with heartbeat and error classification
- Expand config-parser with human-readable AJV errors, security validation, and rule type-specific checks

src/services/index.ts

@@ -0,0 +1,20 @@
+// Copyright (C) 2025 Keygraph, Inc.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License version 3
+// as published by the Free Software Foundation.
+
+/**
+ * Services Module
+ *
+ * Exports DI container and service classes for Shannon agent execution.
+ * Services are pure domain logic with no Temporal dependencies.
+ */
+
+export { Container, getOrCreateContainer, removeContainer } from './container.js';
+export type { ContainerDependencies } from './container.js';
+
+export { ConfigLoaderService } from './config-loader.js';
+export { ExploitationCheckerService } from './exploitation-checker.js';
+export { AgentExecutionService } from './agent-execution.js';
+export type { AgentExecutionInput } from './agent-execution.js';