v0.4.12 — CI credibility + install smoke test

What's new

Added

• .github/workflows/quality.yml — CI shell syntax check. Runs bash -n on install.sh and release.sh, then syntax-checks all .sh files by shebang (bash vs zsh), excluding backups/. shellcheck runs warn-only on bash scripts.
• scripts/install-smoke.sh — local install smoke test. Covers install.sh --help, install.sh --dry-run, bash -n / zsh -n on all scripts, mqlaunch doctor --json, and mqlaunch selftest.
• Proof section in README listing what is verified: dry-run support, release validation gates, JSON health report, selftest, publish readiness gate, HAL read-only commands, and CI syntax coverage.
• terminal/menus/mq-agent-menu.sh — mq-agent submenu (g. Agent) reachable from the main menu with 10 commands across repo analysis, AI, and environment groups.

Changed

• Main menu panel: added g. Agent quick access slot.
• mqlaunch.sh: sources mq-agent-menu.sh when present.
• mq-main-menu.sh: routes g/G and text aliases (agent, score, signal, audit, doctor) to mq-agent menu.
• README version badge bumped to 0.4.12.