#25929 ci: rename the compile status to cmux-next/compile

Leo: "just rename it bro"

What changes

• The PR compile status job (compile-status, shown as "cmux-next fleet Release compile") now publishes the commit status cmux-next/compile.
• For the transition it posts every state twice: under cmux-next/compile and under the previous context name, cmux-next/linux-compile. A reader that still reads the old name keeps working, and nothing goes red. A follow-up PR drops the old name once every reader takes the new one.
• The job's steps, error titles and status descriptions, and the comments around the compile check, the REF capture steps, the route filter and the base-compile revert, use neutral wording ("the compile check", "the fleet build"). Behavior is unchanged apart from the second context.
• Two step names change: "Decide the fleet build's REF capture" and "Capture the fleet build's REF". Their one reader, tests/test_ci_no_github_token_polling.py, is updated.
• nightly.yml's web-bundle and notices job is renamed build-nightly-inputs, its artifacts cmux-nightly-web-bundles and cmux-nightly-notices, and its script scripts/ci/nightly_inputs.py, so the names say what they hold. Upload and download change together in the same workflow, and a missing hand-off already falls back to building on the Mac, so a run in flight loses at most that saving. The download steps, warning titles, hand-off messages, .github/nightly-step-coverage.json and tests/test_nightly_helpers_beside_release_build.py are updated to match.
• The test file is renamed to tests/test_ci_cmux_next_compile_status.py, and tests/test-execution.toml and the workflow's guard step are updated to match. It now checks that each state is posted under both contexts with the same state and link.

Readers checked

• The feat-cmux-next rulesets name no status check, so no required-check entry needs a change.
• The landing tools that read the status are moving to accept both names in their own repository. The old context stays until they have landed.

Risk

Low. The only behavior change is a second status post per state. A failed post on either context still fails the job, as a failed post did before.

Tests

• tests/test_ci_cmux_next_compile_status.py, tests/test_cmux_next_route.py, tests/test_ci_no_github_token_polling.py, tests/test_cmux_next_hybrid_ref_capture.py, tests/test_ci_cmux_next_compile_revert.py, tests/test_dev_landing_place.py, tests/test_nightly_helpers_beside_release_build.py, tests/test_nightly_step_coverage.py, tests/test_nightly_delivery_concurrency.py and tests/test_cmux_next_checks_workflow.py (158 tests) pass locally. tests/test_ci_workflow_guards_are_wired.py fails the same way on base (two unrelated unwired tests).
• scripts/cmux-next/tests/bundle-resources-layout.test.sh passes.
• actionlint reports only the existing unknown-runner-label notice.

Agent session: agent session

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