fix: rescue gnomAD genes with non-Ensembl IDs via gene_symbol fallback

gnomAD v4.1 gene_id column is mixed: ~101K Ensembl IDs + ~111K NCBI numeric.
Now falls back to gene_symbol → gene_universe lookup for non-ENSG entries.

Coverage: 78.5% → 90.3% (17,875 → 20,555 genes with gnomAD scores).
Sufficient evidence (≥4 layers): 19,946 → 20,683 genes.
Validation median percentile: 79.9% → 81.1%.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

data/report/reproducibility.json

@@ -1,6 +1,6 @@
 {
-  "run_id": "e7486ff1-f9be-403b-a68d-115fc845f4a1",
-  "timestamp": "2026-02-15T21:13:12.288563+00:00",
+  "run_id": "093b405b-5a20-4f35-b5b8-04f02451789d",
+  "timestamp": "2026-02-15T21:49:14.940206+00:00",
   "pipeline_version": "0.1.0",
   "parameters": {
     "gnomad": 0.2,
@@ -49,9 +49,9 @@
   ],
   "validation_metrics": {},
   "tier_statistics": {
-    "total": 21103,
-    "high": 18,
-    "medium": 9577,
-    "low": 11508
+    "total": 21177,
+    "high": 82,
+    "medium": 9626,
+    "low": 11469
   }
 }