Cover previously unreachable error paths in New(), GetAll(), and Render():
- New: schema conflict when index named "kv" pre-exists
- GetAll: scan error via NULL-key injection after table restructure
- GetAll: rows iteration error via database page corruption
- Render: scan error via same NULL-key technique
- Render: rows iteration error via same corruption technique
GetAll and Render now at 100%. Only 3 stmts remain uncovered in New()
(sql.Open lazy-error and PRAGMA busy_timeout — both genuinely
unreachable without driver mocking).
Co-Authored-By: Charon <charon@lethean.io>
