fix(infra): attach docker-compose.infra.yml services to molecule-monorepo-net

Closes partially #15 (network-split side of the same incident class).

Running `docker compose -f docker-compose.infra.yml up -d` puts postgres,
redis, clickhouse, langfuse (and the new temporal service) on a fresh
`molecule-monorepo_default` bridge network, while the platform container
lives on `molecule-monorepo-net` (created by the root docker-compose.yml).
Platform then fails DNS on `postgres:5432` and crashes until the
operator manually `docker network connect`s each service.

Declare `molecule-monorepo-net` as the external default network for the
infra compose file so new services join it automatically.

Also adds temporal + temporal-ui services (closes the 'Temporal unavailable'
noise that every agent logs at startup) and exposes the UI on :8233.

Incident: 2026-04-13 — running `up -d temporal` recreated postgres into
the wrong network and took the platform + all 12 workspace agents offline
until networks were manually reconnected.

docker-compose.infra.yml

@@ -65,6 +65,37 @@ services:
       timeout: 5s
       retries: 10
 
+  temporal:
+    image: temporalio/auto-setup:1.25
+    depends_on:
+      postgres:
+        condition: service_healthy
+    environment:
+      DB: postgres12
+      DB_PORT: 5432
+      POSTGRES_USER: ${POSTGRES_USER:-dev}
+      POSTGRES_PWD: ${POSTGRES_PASSWORD:-dev}
+      POSTGRES_SEEDS: postgres
+      DBNAME: temporal
+      VISIBILITY_DBNAME: temporal_visibility
+    ports:
+      - "7233:7233"
+    healthcheck:
+      test: ["CMD", "tctl", "--address", "temporal:7233", "cluster", "health"]
+      interval: 10s
+      timeout: 5s
+      retries: 10
+
+  temporal-ui:
+    image: temporalio/ui:2.31.2
+    depends_on:
+      - temporal
+    environment:
+      TEMPORAL_ADDRESS: temporal:7233
+      TEMPORAL_CORS_ORIGINS: http://localhost:8233
+    ports:
+      - "8233:8080"
+
   langfuse-web:
     image: langfuse/langfuse:2
     depends_on:
@@ -84,6 +115,11 @@ services:
     ports:
       - "3001:3000"
 
+networks:
+  default:
+    name: molecule-monorepo-net
+    external: true
+
 volumes:
   pgdata:
   redisdata: