ci(rust): convert rust-ci.yml to thin wrapper (standards#174) (#19)

Replaces the per-repo `rust-ci.yml` copy with a 5-line wrapper invoking
the shared reusable workflow in `hyperpolymath/standards` (PR #174).

Pinned to PR #174's HEAD SHA `4fdf4314b4ab54269adbaff10e30e483b5e86845`; will resolve to standards/main
once #174 merges.

Estate audit found ~87 rust-ci.yml copies across the estate; this is
one of them. The reusable provides identical cargo check/clippy/fmt/test
behaviour with opt-in `enable_audit` + `enable_coverage` inputs.

Pattern precedent: standards#168 (governance-reusable) + downstream
wrappers absolute-zero#41 + tma-mark2#41.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath