feat: add agent mode for automation scenarios

- Add agent mode that always triggers without checking for mentions
- Implement Mode interface with support for mode-specific tool configuration
- Add getAllowedTools() and getDisallowedTools() methods to Mode interface
- Simplify tests by combining related test cases
- Update documentation and examples to include agent mode
- Fix TypeScript imports to prevent circular dependencies

Agent mode is designed for automation and workflow_dispatch scenarios
where Claude should always run without requiring trigger phrases.

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

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

src/modes/agent/index.ts

@@ -0,0 +1,42 @@
+import type { Mode } from "../types";
+
+/**
+ * Agent mode implementation.
+ *
+ * This mode is designed for automation and workflow_dispatch scenarios.
+ * It always triggers (no checking), allows highly flexible configurations,
+ * and works well with override_prompt for custom workflows.
+ *
+ * In the future, this mode could restrict certain tools for safety in automation contexts,
+ * e.g., disallowing WebSearch or limiting file system operations.
+ */
+export const agentMode: Mode = {
+  name: "agent",
+  description: "Automation mode that always runs without trigger checking",
+
+  shouldTrigger() {
+    return true;
+  },
+
+  prepareContext(context, data) {
+    return {
+      mode: "agent",
+      githubContext: context,
+      commentId: data?.commentId,
+      baseBranch: data?.baseBranch,
+      claudeBranch: data?.claudeBranch,
+    };
+  },
+
+  getAllowedTools() {
+    return [];
+  },
+
+  getDisallowedTools() {
+    return [];
+  },
+
+  shouldCreateTrackingComment() {
+    return true;
+  },
+};