feat(shared,api): add pause + sort_order columns and contracts

Adds server-side pause accounting and activity ordering primitives.
- WorkSession contract gains paused_seconds (number) and paused_at (ISO string | null).
- Activity contract gains sort_order (number); new ReorderActivitiesInput zod.
- work_sessions += paused_seconds (int NOT NULL DEFAULT 0) + paused_at (timestamp_ms nullable).
- activities += sort_order (int NOT NULL DEFAULT 0).
- toWorkSession / toActivity map the new fields; generated migration 0003.

The new fields are additive; existing api/worker/admin tests stay green.

Products affected: SoleLog backend (apps/api), shared contracts (packages/shared)

apps/api/src/routes/activities.ts

@@ -16,6 +16,7 @@ function toActivity(row: ActivityRow): Activity {
     name: row.name,
     insole_types: row.insoleTypes as Activity['insole_types'],
     created_at: new Date(row.createdAt).toISOString(),
+    sort_order: row.sortOrder ?? 0,
   };
 }