Q1-Q8 single-node runner: add matrix orchestrator script

[ShuhaoZhangTony]

Task

Implement a single orchestrator to run Q1~Q8 in single-node mode.

Requirements

• New entrypoint (e.g., scripts/run_q_matrix.py)
• Run order: Q1..Q8
• Standard flags: --backend, --seed, --parallelism, --repeat, --output-dir, --quick
• Force single-node defaults: --nodes 1
• Continue-on-error mode and fail-fast mode
• Per-Q logs and status summary

Acceptance Criteria

• One command can run all Q workloads locally
• Each Q writes unified_results.jsonl/csv under results/q*/
• Exit code reflects overall matrix status

[ShuhaoZhangTony]

实现已提交至 #28：支持显式 --continue-on-error / --fail-fast，任一 workload 失败时矩阵最终返回非零退出码，并为每次运行保留 run.log 和增量 matrix_status.json。

本 Issue 由 #28 在合并后自动关闭；在 PR 合并前不提前宣称完成。