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;

apps/api/prisma/schema.prisma

@@ -261,12 +261,13 @@ model UserPreference {
 }
 
 model Workspace {
-  id        String   @id @default(uuid()) @db.Uuid
-  name      String
-  ownerId   String   @map("owner_id") @db.Uuid
-  settings  Json     @default("{}")
-  createdAt DateTime @default(now()) @map("created_at") @db.Timestamptz
-  updatedAt DateTime @updatedAt @map("updated_at") @db.Timestamptz
+  id           String   @id @default(uuid()) @db.Uuid
+  name         String
+  ownerId      String   @map("owner_id") @db.Uuid
+  settings     Json     @default("{}")
+  matrixRoomId String?  @map("matrix_room_id")
+  createdAt    DateTime @default(now()) @map("created_at") @db.Timestamptz
+  updatedAt    DateTime @updatedAt @map("updated_at") @db.Timestamptz
 
   // Relations
   owner                        User                          @relation("WorkspaceOwner", fields: [ownerId], references: [id], onDelete: Cascade)