feat: implement Claude Code GitHub Action v1.0 with auto-detection and slash commands

Major features:
- Mode auto-detection based on GitHub event type
- Unified prompt field replacing override_prompt and direct_prompt
- Slash command system with pre-built commands
- Full backward compatibility with v0.x

Key changes:
- Add mode detector for automatic mode selection
- Implement slash command loader with YAML frontmatter support
- Update action.yml with new prompt input
- Create pre-built slash commands for common tasks
- Update all tests for v1.0 compatibility

Breaking changes (with compatibility):
- Mode input now optional (auto-detected)
- override_prompt deprecated (use prompt)
- direct_prompt deprecated (use prompt)

src/modes/registry.ts

@@ -1,13 +1,8 @@
 /**
- * Mode Registry for claude-code-action
+ * Mode Registry for claude-code-action v1.0
  *
- * 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/new-mode/)
- * 3. Import and add it to the modes object below
- * 4. Update action.yml description to mention the new mode
+ * This module provides access to all available execution modes and handles
+ * automatic mode detection based on GitHub event types.
  */
 
 import type { Mode, ModeName } from "./types";
@@ -15,41 +10,44 @@ import { tagMode } from "./tag";
 import { agentMode } from "./agent";
 import { reviewMode } from "./review";
 import type { GitHubContext } from "../github/context";
-import { isAutomationContext } from "../github/context";
+import { detectMode, type AutoDetectedMode } from "./detector";
 
-export const DEFAULT_MODE = "tag" as const;
-export const VALID_MODES = ["tag", "agent", "experimental-review"] as const;
+export const VALID_MODES = ["tag", "agent", "review"] as const;
 
 /**
- * All available modes.
- * Add new modes here as they are created.
+ * All available modes in v1.0
  */
 const modes = {
   tag: tagMode,
   agent: agentMode,
-  "experimental-review": reviewMode,
-} as const satisfies Record<ModeName, Mode>;
+  review: reviewMode,
+} as const satisfies Record<AutoDetectedMode, Mode>;
 
 /**
- * Retrieves a mode by name and validates it can handle the event type.
- * @param name The mode name to retrieve
- * @param context The GitHub context to validate against
- * @returns The requested mode
- * @throws Error if the mode is not found or cannot handle the event
+ * Automatically detects and retrieves the appropriate mode based on the GitHub context.
+ * In v1.0, modes are auto-selected based on event type.
+ * @param context The GitHub context
+ * @param explicitMode Optional explicit mode override (for backward compatibility)
+ * @returns The appropriate mode for the context
  */
-export function getMode(name: ModeName, context: GitHubContext): 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.`,
-    );
+export function getMode(
+  context: GitHubContext,
+  explicitMode?: string,
+): Mode {
+  let modeName: AutoDetectedMode;
+
+  if (explicitMode && isValidModeV1(explicitMode)) {
+    console.log(`Using explicit mode: ${explicitMode}`);
+    modeName = mapLegacyMode(explicitMode);
+  } else {
+    modeName = detectMode(context);
+    console.log(`Auto-detected mode: ${modeName} for event: ${context.eventName}`);
   }
 
-  // Validate mode can handle the event type
-  if (name === "tag" && isAutomationContext(context)) {
+  const mode = modes[modeName];
+  if (!mode) {
     throw new Error(
-      `Tag mode cannot handle ${context.eventName} events. Use 'agent' mode for automation events.`,
+      `Mode '${modeName}' not found. This should not happen. Please report this issue.`,
     );
   }
 
@@ -57,10 +55,29 @@ export function getMode(name: ModeName, context: GitHubContext): Mode {
 }
 
 /**
- * Type guard to check if a string is a valid mode name.
+ * Maps legacy mode names to v1.0 mode names
+ */
+function mapLegacyMode(name: string): AutoDetectedMode {
+  if (name === "experimental-review") {
+    return "review";
+  }
+  return name as AutoDetectedMode;
+}
+
+/**
+ * Type guard to check if a string is a valid v1.0 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);
+export function isValidModeV1(name: string): boolean {
+  const v1Modes = ["tag", "agent", "review", "experimental-review"];
+  return v1Modes.includes(name);
+}
+
+/**
+ * Legacy type guard for backward compatibility
+ * @deprecated Use auto-detection instead
+ */
+export function isValidMode(name: string): name is ModeName {
+  return isValidModeV1(name);
 }