[codeandsolder]

Finish the maintenance queue instead of waiting on thin wrapper crates to catch up.

Changes:

• upgrade testcontainers 0.27 -> 0.28 and remove testcontainers-modules; the E2E Postgres fixture now uses GenericImage directly with the same image tag, port, readiness messages, postgres credentials, and fsync=off behavior
• upgrade validator 0.20 -> 0.21 and remove axum-valid; login/refresh handlers deserialize with Axum and call Validate::validate() directly, preserving generic 400 validation failures
• refresh Cargo.lock
• fix the passive maintenance workflow so Markdown backticks in generated issue bodies are escaped instead of being evaluated as shell command substitutions

Branch validation already completed successfully with Rust 1.98.1: cargo update, cargo fmt --all, and cargo check --locked -p gateway-example -p e2e-tests --lib.

Closes #14
Closes #16
Closes #19