Repair harness slot layout migration on existing databases

[rullopat]

Summary

• restore migration 0009 to its originally shipped Team-slot schema
• add forward migration 0013 for optional slot layout columns
• make 0013 converge both older databases missing the columns and interim fresh databases that already contain them
• add an upgrade-path regression test

User-visible fix

Creating or opening a Team template on an upgraded installation no longer fails because position_x is missing.

Verification

• repaired the live ~/.bazilion database and verified both slot tables
• Team listing succeeds against the repaired daemon
• focused migration, harness, and route tests: 32 passed
• full repository suite: 95 files, 744 tests passed
• root typecheck
• git diff --check