feat(llm): 引入 rig-core 并建立新 LLM 门面（Ollama 首个打通）

- 依赖改用 rig-core 0.41（仅 reqwest+rustls，不引入 agent/derive）
- 新门面：provider 枚举 + 统一配置 + 单一生成入口 + 凭据校验 + 错误映射
- Ollama 走 rig /api/chat，参数映射与错误文案与旧实现一致
- 用 rig 请求录制 mock 断言请求形状；8 个新单元测试

Cargo.toml

@@ -34,7 +34,7 @@ which = "6.0"
 
 # HTTP client for LLM APIs
 reqwest = { version = "0.12", features = ["json", "rustls-tls", "stream"], default-features = false }
-tokio = { version = "1.35", features = ["full"] }
+tokio = { version = "1.35", features = ["full", "macros", "rt-multi-thread"] }
 
 # Error handling
 thiserror = "1.0"
@@ -76,6 +76,8 @@ edit = "0.1"
 
 # Shell completion generation
 shell-words = "1.1"
+# LLM integration (rig-core only: HTTP backend + rustls; no agent/derive)
+rig-core = { version = "0.41", default-features = false, features = ["reqwest", "rustls"] }
 
 [dev-dependencies]
 assert_cmd = "2.0"
@@ -83,6 +85,9 @@ predicates = "3.1"
 tempfile = "3.9"
 mockall = "0.12"
 wiremock = "0.6"
+# rig mock HTTP backends for LLM layer tests
+rig-core = { version = "0.41", default-features = false, features = ["test-utils"] }
+http = "1"
 
 [profile.release]
 opt-level = "s"