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)

package.json

@@ -16,6 +16,8 @@
     "@octokit/graphql": "^8.2.2",
     "@octokit/rest": "^21.1.1",
     "@octokit/webhooks-types": "^7.6.1",
+    "@types/js-yaml": "^4.0.9",
+    "js-yaml": "^4.1.0",
     "node-fetch": "^3.3.2",
     "zod": "^3.24.4"
   },