fix(docker): unbreak the arm64 image build under Rust 1.98

[henry40408]

The Docker workflow has been failing on main since #510 bumped the toolchain to Rust 1.98. Only the arm64 leg is affected; amd64 builds fine.

Cause

Rust 1.98 passes -Wl,--fix-cortex-a53-843419 as a pre-link arg for aarch64-unknown-linux-musl (rust-lang/rust#155453). zig's linker does not accept it:

error: linking with `/root/.cache/cargo-zigbuild/0.22.3/wrappers/6f7f/zigcc-aarch64-unknown-linux-musl-5d3b.sh` failed: exit status: 1
  = note: error: unsupported linker arg: --fix-cortex-a53-843419
error: could not compile `rdrs` (bin "rdrs") due to 1 previous error

Failing run on main: https://github.com/henry40408/rdrs/actions/runs/33187487621

cargo-zigbuild filters that arg out as of rust-cross/cargo-zigbuild#452, first released in 0.23.0. The Dockerfile pinned 0.22.3, which predates the fix.

Change

ZIGBUILD_VERSION 0.22.3 → 0.23.0. 0.23.1 through 0.23.3 all landed within the last seven days and are inside this repo's dependency cooldown; 0.23.0 (published 2026-06-16) is the oldest release carrying the fix, and is what noadd, pingward and liftlog already pin.

ZIG_VERSION stays at 0.14.1 — 0.23.0 still supports it, and the libc++-19 bindgen caveat in the existing comment only applies to zig 0.15+.

Verification

docker.yml only fires on pushes to main and on tags, so this PR's own checks do not exercise the cross-compile. Verified locally instead:

$ docker buildx build --platform linux/arm64 --target build \
    --build-arg GIT_VERSION=v0.81.1-3-g70c2e57 .
#15 128.1     Finished `release` profile [optimized] target(s) in 2m 01s
#15 128.2 + install -Dm755 target/aarch64-unknown-linux-musl/release/rdrs /out/rdrs
#15 DONE 128.3s

The build emits one benign warning from zig — linker stderr: ignoring deprecated linker optimization setting '1' — which does not fail the build.

No Rust test accompanies this change: it is a single build-argument edit in the Dockerfile, unreachable from the project's test harness and exercised only by the Docker workflow.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.52%. Comparing base (70c2e57) to head (a9d48c4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #521   +/-   ##
=======================================
  Coverage   93.52%   93.52%           
=======================================
  Files          87       87           
  Lines       25896    25896           
=======================================
  Hits        24218    24218           
  Misses       1678     1678           

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