Polish drug harmonizer dashboard

[JessicaMaine]

Summary

• Rework the Drug Harmonizer dashboard to match the Disease Explorer dashboard structure and styling
• Add drug-specific harmonization metrics: loaded/full nodes, multi-source identity coverage, NodeNorm resolution, open QC rows, and target association edges
• Collapse source catalog display to one row per source with source version/date, ODIN download/transform dates, row counts, statuses, and notes
• Add a source-versions API endpoint for dashboard rendering

Validation

• PYTHONPYCACHEPREFIX=/private/tmp/ifx_pycache python -m py_compile src/qa_browser/app.py src/qa_browser/drug_id_graph.py
• GET /drug-id-qa -> 200
• GET /drug-id-qa/api/stats -> 200
• GET /drug-id-qa/api/source-versions -> 200