chore: pin Rust 1.98.0

[coderbants]

The recovered change comes from mutate request 000128-Szal-pin-rust-1-98-0-globally and parent recovery PR https://github.com/stackie-dev/parent/pull/440. The original local mutate worktree contained uncommitted Rust-version selector changes without a per-repository commit; this follow-up records that work against current dev. It pins the package MSRV, checked toolchain, CI, publish workflow, and contributor instructions to Rust 1.98.0. No runtime behavior changes.

Verification: cargo test --all-targets --no-fail-fast; cargo fmt --all --check; git diff --check.

[coderbants]

Quorum review complete for exact head c2d2e43287b543b90d15641330f2d8d9d2f1f368.

• Engineering: GREEN
• Testing: GREEN
• Domain/workflow: GREEN
• Security: GREEN
• Focused checks: shell syntax, release guards, matching-version and negative-tag checks, forbidden-token scan, and diff check passed.
• Available exact-head CI: Version Change Required, Lint / Build / Doc / Tests, and Coverage passed. Update coverage badge is intentionally skipped for pull requests because it is restricted to pushes to dev.

The review journal remains local/untracked and was not included in the change.