feat: add db schema, init, and vitest config

documentation/data-pipeline.md

@@ -528,6 +528,7 @@ llama.cpp is not installed.
 
 **Next action:** Write the round 1 generation script.
 
+- [ ] Write tests for stage 3
 - [ ] Write round 1 script (generation)
 - [ ] Write compile-candidates script
 - [ ] Write round 2 script (voting)
@@ -542,24 +543,28 @@ llama.cpp is not installed.
 
 ### Stage 4 — Merge `🔲 not started`
 
+- [ ] Write tests for stage 3
 - [ ] Write merge script
 - [ ] Run merge → `pipeline.db`
 - [ ] Confirm tiebreaker resolves all flagged translations
 
 ### Stage 4b — Tiebreak `🔲 not started`
 
+- [ ] Write tests for stage 3
 - [ ] Write tiebreak logic
 - [ ] Run tiebreaker for all flagged translations
 - [ ] Confirm no flagged translations remain before seeding
 
 ### Stage 5 — Compare / QA `🔲 not started`
 
+- [ ] Write tests for stage 3
 - [ ] Write compare script
 - [ ] Run compare → `COVERAGE.md`
 - [ ] Review output quality before seeding
 
 ### Stage 6 — Sync `🔲 not started`
 
+- [ ] Write tests for stage 3
 - [ ] Write sync script
 - [ ] Configure `DATABASE_URL` in `.env`
 - [ ] Run sync → production PostgreSQL