feat(skills): WASM host 函数真实实现 — zclaw_log/http_fetch/file_read (Phase 4B)

替换 stub 为真实实现:
- zclaw_log: 读取 guest 内存并 log
- zclaw_http_fetch: ureq v3 同步 GET (10s timeout, network_allowed 守卫)
- zclaw_file_read: 沙箱 /workspace 目录读取 (路径校验防逃逸)
添加 ureq v3 workspace 依赖, 25 测试全通过。

Cargo.toml

@@ -63,6 +63,9 @@ libsqlite3-sys = { version = "0.27", features = ["bundled"] }
 # HTTP client (for LLM drivers)
 reqwest = { version = "0.12", default-features = false, features = ["json", "stream", "rustls-tls"] }
 
+# Synchronous HTTP (for WASM host functions in blocking threads)
+ureq = { version = "3", features = ["rustls"] }
+
 # URL parsing
 url = "2"