fix(deps): bump tokio-postgres to 0.7.18

[tobyhede]

Summary

Bumps tokio-postgres in Cargo.lock from 0.7.13 → 0.7.18 to address GHSA-3gjw-f78c-vvpw (Medium; affected >= 0.4.0, < 0.7.18). Resolves Dependabot alert #55.

Lockfile-only change; no Cargo.toml edits (all manifests already use tokio-postgres = "0.7").

Lockfile changes

• tokio-postgres 0.7.13 → 0.7.18
• Companion/transitive bumps pulled in by the resolver: postgres-types 0.2.9 → 0.2.14, postgres-derive 0.4.6 → 0.4.9, whoami 1.6.0 → 2.1.3, wasite 0.1.0 → 1.0.2, phf/phf_shared 0.11.3 → 0.13.1, serde_json 1.0.140 → 1.0.151; added objc2-core-foundation, objc2-system-configuration, zmij
• libredox 0.1.3 → 0.1.24 (required: whoami 2.x needs a newer libredox than was locked)
• postgres-protocol (0.6.12) and tokio-postgres-rustls (0.13.0) unchanged

Verification

• cargo tree -i tokio-postgres --workspace: single version, tokio-postgres v0.7.18
• cargo check --workspace --all-targets: passes