fix(aibox): never fall back to deepseek.key for model profile endpoints (H1)

~/.cert/deepseek.key is a DeepSeek-only credential; when a models profile
specified its own api_key_env (e.g. MOONSHOT_API_KEY) but the env var was
unset, resolve_api_key silently read that file and sent the DeepSeek key
as Bearer to a third-party endpoint (cross-vendor credential leak).

resolve_api_key gains allow_key_file (default True for the legacy flat
api section); create_llm_client passes allow_key_file=profile is None so
any profile path raises a clear RuntimeError instead, pointing users to
set the env var or use "" for local keyless endpoints.

Tests: new TestH1KeyIsolation (4 cases) with a mocked readable
deepseek.key proving the profile path errors out while the flat api
section still reads the file; full suite 276 passed.

aibox/README.md

@@ -548,7 +548,7 @@ AI 可以通过 `update_soul` 工具动态更新 `99_SOUL.md`，通过 `update_i
 |---|---|
 | `api_url` | 端点 URL（OpenAI Chat Completions 协议） |
 | `model` | 该档案使用的模型名 |
-| `api_key_env` | API Key 环境变量名；**未配置回退 `api.api_key_env`；显式空串 `""` 为本地免密端点**（Ollama/vLLM） |
+| `api_key_env` | API Key 环境变量名；**未配置回退 `api.api_key_env`；显式空串 `""` 为本地免密端点**（Ollama/vLLM）。档案端点环境变量取不到时**直接报错，绝不回退 `~/.cert/deepseek.key`**——该文件为 DeepSeek 专属凭据，跨厂商复用属于泄漏（key 文件回退仅对无档案的旧 `api` 扁平节生效） |
 | `reasoning_enabled` | 档案级思考模式开关（缺省回退 `api.reasoning_enabled`） |
 | `timeout` | 请求超时秒数 |