feat(v1.5.0): Relations, Rollups, Formulas — FormulaEngine, RollupEngine, API

- FormulaEngine: 19 functions (prop, if, concat, round, now, today, dateAdd, replace, ...)
- RollupEngine: 12 aggregations (count, sum, avg, min, max, range, unique, percent_checked)
- API relation: POST /db/{id}/properties/relation + /link (bidirectional)
- API rollup: POST /db/rollup/compute
- API formula: POST /db/formula/evaluate
- FKs fix: related_collection_id/relation_property_id/target_property_id → ON DELETE SET NULL
- 43/43 tests passent (+5 tests v1.5)
- Version 1.4.0 → 1.5.0
- Docs: ROADMAP, CHANGELOG à jour

app/routers/api.py

@@ -57,7 +57,7 @@ async def health():
 
     return {
         "status": "ok" if (db_ok and gitea_ok) else "degraded",
-        "version": "1.4.0",
+        "version": "1.5.0",
         "db": db_ok,
         "gitea": gitea_ok,
     }