refactor: src-tauri 重命名为 gui

Tauri CLI 自动检测 workspace 成员，构建不受影响。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gui/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "patheditor"
+version = "5.0.0"
+description = "Windows PATH Environment Variable Editor"
+authors = ["刘航宇"]
+license = "MIT"
+repository = "https://github.com/LHY0125/PathEditor"
+edition = "2021"
+rust-version = "1.77.2"
+
+[lib]
+name = "app_lib"
+crate-type = ["staticlib", "rlib"]
+
+[build-dependencies]
+tauri-build = { version = "2.6.2", features = [] }
+
+[dependencies]
+path-editor-core = { path = "../core" }
+serde_json = "1.0"
+serde = { version = "1.0", features = ["derive"] }
+log = "0.4"
+tauri = { version = "2.11.2", features = [] }
+tauri-plugin-log = "2"
+tauri-plugin-dialog = "2"