feat: add agent mode for automation scenarios (#337)

* 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>

* Minor update to readme (from @main to @beta)

* Since workflow_dispatch isn't in the base action, update the examples accordingly

* minor formatting issue

* Update to say beta instead of main

* Fix missed tracking comment to be false

---------

Co-authored-by: km-anthropic <km-anthropic@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/modes/registry.ts

@@ -5,17 +5,17 @@
  *
  * To add a new mode:
  * 1. Add the mode name to VALID_MODES below
- * 2. Create the mode implementation in a new directory (e.g., src/modes/review/)
+ * 2. Create the mode implementation in a new directory (e.g., src/modes/new-mode/)
  * 3. Import and add it to the modes object below
  * 4. Update action.yml description to mention the new mode
  */
 
-import type { Mode } from "./types";
-import { tagMode } from "./tag/index";
+import type { Mode, ModeName } from "./types";
+import { tagMode } from "./tag";
+import { agentMode } from "./agent";
 
 export const DEFAULT_MODE = "tag" as const;
-export const VALID_MODES = ["tag"] as const;
-export type ModeName = (typeof VALID_MODES)[number];
+export const VALID_MODES = ["tag", "agent"] as const;
 
 /**
  * All available modes.
@@ -23,6 +23,7 @@ export type ModeName = (typeof VALID_MODES)[number];
  */
 const modes = {
   tag: tagMode,
+  agent: agentMode,
 } as const satisfies Record<ModeName, Mode>;
 
 /**