Update the pinned Rust toolchain from 1.93.0 to 1.97.0 (latest stable,
released 2026-07-09) across the worker/server build Dockerfiles
(Dockerfile, docker/DockerfileFull, docker/DockerfileFullEe) and all CI
workflows that pin a toolchain.
Verified the backend compiles cleanly with 1.97.0 under `-D warnings`
(the default RUSTFLAGS used by actions-rust-lang/setup-rust-toolchain).
Fixes WIN-2155
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>