refactor: 规则中性化——剥离 PPT 业务，统一为订单示范域

把规则从原 ppt-gen 项目泛化为通用脚手架，覆盖 19 个文件：
- ddd/architecture/design-discipline/error-codes/communication-* 等：
  领域术语、错误码、消息示例、扩展点、状态流统一为「订单」示范域
- agent-dag/agent.md/agent-concurrency/agent-llm-*：DAG 节点、配置、并发、
  LLM 适配从「对话→预览→生成→截图→合成」改为「intake→process→validate→finalize」
- backend-db：Session 实体/状态机/ORM/仓储/checkpoint 对齐新流水线
- 移除幻灯片专属依赖与产物：agent 去 playwright/python-pptx，
  Dockerfile 去 Chromium 系统库，.gitignore 去 *.pptx
- 保留合法通用项：ANSI（PTY 处理）、Playwright（E2E 测试工具）、Gemini CLI（真实 provider）

验证：gemini-cli/openai-api 两变体生成退出 0，生成项目零 PPT 残留，
backend/agent 骨架均可 import 运行。

template/agent/pyproject.toml.jinja

@@ -8,14 +8,12 @@ dependencies = [
     "uvicorn[standard]",
     "loguru",
     "pydantic-settings",
-{%- if llm_provider == 'gemini-cli' %}
-    "playwright",
-    "python-pptx",
-{%- elif llm_provider == 'openai-api' %}
+{%- if llm_provider == 'openai-api' %}
     "openai",
 {%- elif llm_provider == 'anthropic-api' %}
     "anthropic",
 {%- endif %}
+    # 业务相关外部能力（导出、第三方 SDK 等）按需自行 uv add
 ]
 
 [dependency-groups]
@@ -50,4 +48,4 @@ root_packages = ["src"]
 name = "Domain zero IO"
 type = "forbidden"
 source_modules = ["src.domain"]
-forbidden_modules = ["fastapi", "httpx", "subprocess", "playwright"]
+forbidden_modules = ["fastapi", "httpx", "subprocess"]