PGx DB: pgx db build from CPIC (PGX-001..005, IN-053, CLI-035)

- scripts/pgx/fetch_sources.sh: CPIC API tables (CC0) into a dated folder with version and hashes.
- simurg/pgx/db.py: CPIC HGVS locations and values -> left-normalised VCF variants (SNV, del, ins, dup,
  repeats, delins, chrM); IUPAC values are core-allele wildcards; alleles without definitions are flagged.
- pipeline/pgx_db.py: deterministic SQLite (content-hash name), probe_map via the SNV VCF site mapper;
  GSA v4 PGx: 22 genes, 1354 alleles, 5002 probe links; two builds byte-identical.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01814GKVzZVL3FuF3DeiZXhv

docs/messages.md

@@ -44,6 +44,7 @@ Generated from `src/simurg/core/errors.py` — do not edit by hand.
 | `E_OUTPUT_EXISTS` | error | Outputs already exist; use --force or --resume | CLI-010 |
 | `E_PGX_BATCH_TOO_SMALL` | error | Too few (passing) samples in the batch for PGx CN calling | PCN-004 |
 | `E_PGX_CN_FAILED` | error | PGx CN calling failed for the sample | PCN-002 |
+| `E_PGX_SOURCE` | error | PGx source tables missing; run scripts/pgx/fetch_sources.sh | PGX-001 |
 | `E_PGX_TRAIN_TOO_SMALL` | error | Too few (passing) samples to train a PGx CN model | PCN-005 |
 | `E_QC_CONFIG_EXT` | error | QC config file must be .yaml or .yml | QC-021 |
 | `E_QC_CONFIG_MISSING` | error | QC config file does not exist | QC-021 |