Add .gitignore to .beads directory during init (#64)

- Create .gitignore file in .beads/ when running bd init
    - Ignores *.db and *.db-* patterns to prevent database commits
    - Add test coverage to verify .gitignore creation
    - Add .claude/settings.local.json to project .gitignore

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

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

Co-authored-by: Ben Madore <madorb@users.noreply.github.com>

.gitignore

@@ -20,6 +20,9 @@ go.work
 *.swo
 *~
 
+# Claude Code
+.claude/settings.local.json
+
 # OS
 .DS_Store
 Thumbs.db