Share PostgreSQL profile ownership with Batter foundation

[featherenvy]

Summary

• Delegate RunledgerDatabase pool/profile ownership to batter-sqlx PgProfiledPool, preserving public APIs and one-schema validation.
• Pin the shared foundation checkpoint used by Batter PR Bump actions/checkout from 4.3.1 to 6.0.2 #3; avoid copying mandatory connect/acquire/release hooks into another adapter.
• Make the source-pin regression read its fixture dependency revision instead of a historical hash.

Validation

• Six PostgreSQL 18.6 profile regressions and five source-guard regressions pass.
• All 374 PostgreSQL and 497 runtime tests/doctests pass.
• PostgreSQL all-target Clippy, formatting and nine packaged-consumer smoke tests pass.
• Native review of a8f6283..a5048e4 reported no findings; all five hosted CI jobs pass.

No migrations or queue behavior changes. The existing runledger-wtb tracker import conflict is documented and untouched. Merge this companion before Batter PR #3; neither PR was merged by the implementation workflow.