fix: restore gnomAD and expression evidence layers for complete 6-layer scoring

Three bugs prevented gnomAD and expression data from contributing to scores:
1. gnomAD COLUMN_VARIANTS mapped "gene" (HGNC symbol) to gene_id instead of
   gene_symbol, causing JOIN miss with gene_universe (Ensembl IDs)
2. Expression HPA data was fetched but never merged (lf_hpa unused)
3. GTEx versioned Ensembl IDs (ENSG*.5) didn't match gene_universe

Results: gnomAD 78.5% coverage, expression 87.4%, 19946 genes with ≥4 layers.
HIGH tier refined from 44 → 18 candidates. Validation PASSED (CDH23 96.5th pctl).

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

data/report/reproducibility.md

@@ -1,7 +1,7 @@
 # Pipeline Reproducibility Report
 
-**Run ID:** `0bcdae80-84c2-486b-809a-36040ce4821d`
-**Timestamp:** 2026-02-15T20:47:54.482074+00:00
+**Run ID:** `e7486ff1-f9be-403b-a68d-115fc845f4a1`
+**Timestamp:** 2026-02-15T21:13:12.288563+00:00
 **Pipeline Version:** 0.1.0
 
 ## Parameters
@@ -39,7 +39,7 @@
 
 ## Tier Statistics
 
-- **Total Candidates:** 19342
-- **HIGH:** 44
-- **MEDIUM:** 7268
-- **LOW:** 12030
+- **Total Candidates:** 21103
+- **HIGH:** 18
+- **MEDIUM:** 9577
+- **LOW:** 11508