[codex] Add combined Test-B and Test-C data

[xdedlhqhw]

Summary

• add one compressed PostgreSQL export containing Test-B and Test-C
• preserve the two splits as separate tactic_step and tactic_step_2 tables
• document table schemas, row counts, checksum, validation, and restore commands
• keep the legacy Test-B-only archive for backward compatibility

Privacy and reproducibility

• normalize Test-C source-machine URI prefixes to repository-relative paths
• omit database owner and ACL statements
• track the 194 MB archive with Git LFS

Validation

• gzip -t data/test_sets_B_C_tactic_steps.sql.gz
• SHA-256: a26170707fbf63cf32c4597e9f63d2b050b1c9807eb0bf1c9e88839e7b64e036
• restored into a temporary PostgreSQL database and verified 8,288 Test-B rows and 12,494 Test-C rows
• verified zero absolute /Users/ URIs after restoration
• uploaded the LFS object successfully and confirmed it is downloadable from a fresh clone