Add unit tests for account_name parser

Tests cover:
- Valid account names (simple, with numbers, dots, hyphens)
- Invalid account names (too short, too long, uppercase, starting with number, special chars)
- PERFORM_WORKING_ACCOUNT_LOAD placeholder passes without validation

Tests follow AAA (Arrange, Act, Assert) pattern.

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

)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>