Workload: Nightly execution and signal review workflow

[dexcompiler]

Epic: #58

Type: Infra | Signal area: Performance, Reliability | Runtime mode: N/A

Deliver

Scheduled (and optionally on-demand) scenario runs, artifact retention, trendline tracking, and documented regression thresholds.

Signals to capture

Slow performance drift and intermittent correctness failures that short PR CI might miss.

Acceptance criteria

Each nightly produces a compact summary of new failures/regressions with links to created issues and retained artifacts.