ci: unify local and GitHub gates

[andreasronge]

Summary

• centralize deterministic gate commands and environment in scripts/ci
• make GitHub Actions, pre-push, Mix aliases, and launcher release validation use the same repository entry points
• enforce CI=1 property parity while retaining native scheduler stress and offering an explicit four-scheduler mode
• reject stale lockfiles before workflow setup can repair them
• make terminal-sensitive tests deterministic through an injected, validated terminal capability
• harden the load-sensitive MCP launcher timeout contract exposed by the unified full-suite gate

Context

This is a main-based follow-up to the CI friction observed on #1339. It does not patch or depend on that PR's branch.

Scope

This PR unifies deterministic core, static, Dialyzer, release, Viewer, documentation, and launcher gates. Ubuntu container parity and the deterministic replay/live-provider split for E2E tests remain focused follow-ups.

Verification

• mix precommit
• scripts/ci/core-tests.sh --schedulers 4 under an attached pseudo-terminal (6,218 tests)
• complete pre-push replay (all seven selected phases passed)
• scripts/ci/launcher.sh
• scripts/ci/docs.sh
• ShellCheck and actionlint
• independent Codex review, including follow-up verification of all findings