test: Add unit tests for mail router and mailbox (gt-1pelm)
Add comprehensive tests for:
- router_test.go: 7 tests covering detectTownRoot, isTownLevelAddress,
addressToSessionID, isSelfMail, shouldBeWisp, resolveBeadsDir
- mailbox_test.go: 17 tests for legacy mailbox operations
- types_test.go: Enhanced with additional priority and message tests
Coverage: 57.8% for mail package (legacy mailbox fully tested,
beads integration requires runtime infrastructure)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
9c718b0d7d