refactor: replace magic number with GITHUB_ACTIONS_BOT_ID constant

- Create new constants file at src/github/constants.ts with GITHUB_ACTIONS_BOT_ID and GITHUB_ACTIONS_BOT_LOGIN
- Replace all occurrences of magic number 41898282 with the constant
- Update imports across source and test files to use the new constants
- Add comment in action.yml referencing the constants file for the default bot_id value

This improves code maintainability by centralizing the GitHub Actions bot ID definition.

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

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

src/github/constants.ts

@@ -0,0 +1,14 @@
+/**
+ * GitHub-related constants used throughout the application
+ */
+
+/**
+ * GitHub Actions bot user ID
+ * This is the official ID for github-actions[bot] used in GitHub repositories
+ */
+export const GITHUB_ACTIONS_BOT_ID = 41898282;
+
+/**
+ * GitHub Actions bot username
+ */
+export const GITHUB_ACTIONS_BOT_LOGIN = "github-actions[bot]";