docs: add SQL function standardization to Phase 1 (NOW→CURRENT_TIMESTAMP)

Author: claude

docs/design/multi-backend-plan.md

@@ -125,7 +125,17 @@ CORE_TYPES = {
 }
 ```
 
-### 1.4 Design Decisions
+### 1.4 SQL Function Standardization
+
+Replaced MySQL-specific `NOW()` with standard SQL `CURRENT_TIMESTAMP` in:
+- `jobs.py` - all timestamp queries
+- `autopopulate.py` - pending job queries
+
+`CURRENT_TIMESTAMP` works identically on MySQL and PostgreSQL.
+
+**Remaining:** `INTERVAL n SECOND` syntax differs between backends and will be handled by the adapter's `interval_expr()` method.
+
+### 1.5 Design Decisions
 
 | Decision | Rationale |
 |----------|-----------|