955 Edge Case Tests & DRY Audit
Two large code health passes in a single day.
Test suite expansion — added 955 edge case tests across backend and frontend, covering auth edge cases, API error paths, component boundary conditions, and hook state transitions.
DRY audit — eliminated ~1,300 duplicate lines across 63 files. Extracted shared helpers, consolidated repeated patterns, and removed copy-pasted logic that had drifted out of sync.