refactor: remove standalone mode, consolidate to managed-only (PostgreSQL) (#70)

- Remove standalone mode code: file-based stores, standalone gateway,
  heartbeat service, SQLite memory, standalone docker-compose
- Rename docker-compose.managed.yml → docker-compose.postgres.yml
- Clean up ~130 Go comments referencing "managed mode" qualifier
- Simplify docker-compose.yml env vars (providers/channels via web UI)
- Update .env.example to essential vars only (token + encryption key)
- Add setup wizard UI (provider → agent → channel bootstrap flow)
- Add logs.tail WebSocket handler for live log streaming
- Add cursor-pointer to interactive UI components
- Clean up config page (remove standalone-only sections)
- Update README and docs for managed-only architecture

docker-compose.postgres.yml

@@ -0,0 +1,40 @@
+# PostgreSQL overlay — pgvector for multi-tenant storage.
+#
+# Usage (with Web Dashboard):
+#   docker compose -f docker-compose.yml -f docker-compose.postgres.yml -f docker-compose.selfservice.yml up -d --build
+#
+# Required env vars (set in .env or shell):
+#   GOCLAW_OPENROUTER_API_KEY (or another provider key)
+#   POSTGRES_PASSWORD (defaults to "goclaw" for dev)
+
+services:
+  postgres:
+    image: pgvector/pgvector:pg18
+    ports:
+      - "${POSTGRES_PORT:-5432}:5432"
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER:-goclaw}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-goclaw}
+      POSTGRES_DB: ${POSTGRES_DB:-goclaw}
+    volumes:
+      - postgres-data:/var/lib/postgresql
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-goclaw}"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+    restart: unless-stopped
+
+  goclaw:
+    depends_on:
+      postgres:
+        condition: service_healthy
+    environment:
+      - GOCLAW_POSTGRES_DSN=postgres://${POSTGRES_USER:-goclaw}:${POSTGRES_PASSWORD:-goclaw}@postgres:5432/${POSTGRES_DB:-goclaw}?sslmode=disable
+    volumes:
+      - goclaw-skills:/app/skills
+      - goclaw-workspace:/app/.goclaw
+
+volumes:
+  postgres-data:
+  goclaw-skills: