[zackees]

Fixes the current ci-lint RUST-015/016/017 findings (ci-lint precheck --local, ci.yml@main). The issue's list was stale: RUST-015 and RUST-016 already report nothing. Only RUST-017 was left.

Findings fixed

• ci-preflight.yml jobs.preflight.steps[18] (Terminal graphics capability matrix): removed --nocapture. The matrix goes to RUNNING_PROCESS_TERMINAL_CAPABILITY_EXPORT_DIR and the next step reads it from there, so stdout isn't needed. libtest still prints the output of a failing test.
• independent-spawn.yml jobs.docker-fixture-build.steps[5] (absent user session bus): removed --nocapture. It runs one test, and its output on failure is still shown.
• ci-preflight.yml jobs.preflight.steps[21] (Broker Hello perf guard): kept --nocapture and added # ci-lint: allow RUST-017 <reason>. It runs a single timing test, so there is nothing to run in parallel, and it shouldn't share cores anyway. The p50/p99 line it prints when it passes is the perf evidence.

Coverage is unchanged: the same tests run with the same filters.

ci-lint before

== RUST-017 (3) ==
[RUST-017] VIOLATION .github/workflows/ci-preflight.yml  jobs.preflight.steps[18]: 'cargo test' passes --nocapture
[RUST-017] VIOLATION .github/workflows/ci-preflight.yml  jobs.preflight.steps[21]: 'cargo test' passes --nocapture
[RUST-017] VIOLATION .github/workflows/independent-spawn.yml  jobs.docker-fixture-build.steps[5]: 'cargo test' passes --nocapture

(no RUST-015 or RUST-016 findings)

ci-lint after

No RUST-015, RUST-016 or RUST-017 findings.

The local gate passed (linux-quick, 877s) and stamped the head.

Refs forge-ci/ci.yml#132