Sprint 238 Plan: Native Decomposition Quality Gate

Goal

Detect and optionally block weak native decomposition before semantic fallback hides generation deficiencies.

Step 2233: Add native decomposition gate packet to pipeline summary.
Step 2234: Support configurable minimum native task count and semantic signal count.
Step 2235: Add optional hard-fail mode for gate violations.
Step 2236: Persist gate artifact for every pipeline run.
Step 2237: Add Sprint238IntegrationSummary.h and execution tracker.