Add mode support (#333)

* Add mode support

* update "as any" with proper "as unknwon as ModeName" casting

* Add documentation to README and registry.ts

* Add  tests for differen event types, integration flows, and error conditions

* Clean up some tests

* Minor test fix

* Minor formatting test + switch from interface to type

* correct the order of mkdir call

* always configureGitAuth as there's already a fallback to handle null users by using the bot ID

* simplify registry setup

---------

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

src/modes/registry.ts

@@ -0,0 +1,52 @@
+/**
+ * Mode Registry for claude-code-action
+ *
+ * This module provides access to all available execution modes.
+ *
+ * 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/)
+ * 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";
+
+export const DEFAULT_MODE = "tag" as const;
+export const VALID_MODES = ["tag"] as const;
+export type ModeName = (typeof VALID_MODES)[number];
+
+/**
+ * All available modes.
+ * Add new modes here as they are created.
+ */
+const modes = {
+  tag: tagMode,
+} as const satisfies Record<ModeName, Mode>;
+
+/**
+ * Retrieves a mode by name.
+ * @param name The mode name to retrieve
+ * @returns The requested mode
+ * @throws Error if the mode is not found
+ */
+export function getMode(name: ModeName): Mode {
+  const mode = modes[name];
+  if (!mode) {
+    const validModes = VALID_MODES.join("', '");
+    throw new Error(
+      `Invalid mode '${name}'. Valid modes are: '${validModes}'. Please check your workflow configuration.`,
+    );
+  }
+  return mode;
+}
+
+/**
+ * Type guard to check if a string is a valid mode name.
+ * @param name The string to check
+ * @returns True if the name is a valid mode name
+ */
+export function isValidMode(name: string): name is ModeName {
+  return VALID_MODES.includes(name as ModeName);
+}