feat(#380): Workspace-to-Matrix-Room mapping and provisioning

- Add matrix_room_id column to workspace table (migration)
- Create MatrixRoomService for room provisioning and mapping
- Auto-create Matrix room on workspace provisioning (when configured)
- Support manual room linking for existing workspaces
- Unit tests for all mapping operations

Refs #380

apps/api/prisma/migrations/20260215000000_add_matrix_room_id/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "workspaces" ADD COLUMN "matrix_room_id" TEXT;