refactor(config): consolidate get_home_dir into single public function

Follow-up to #644: Extract duplicate get_home_dir() implementations
into a single pub fn in config.rs, reducing code duplication across
codex_config.rs, gemini_config.rs, and settings.rs.

Also adds documentation comments to build.rs explaining the Windows
manifest workaround for test binaries.

src-tauri/build.rs

@@ -1,6 +1,16 @@
 fn main() {
     tauri_build::build();
 
+    // Windows: Embed Common Controls v6 manifest for test binaries
+    //
+    // When running `cargo test`, the generated test executables don't include
+    // the standard Tauri application manifest. Without Common Controls v6,
+    // `tauri::test` calls fail with STATUS_ENTRYPOINT_NOT_FOUND.
+    //
+    // This workaround:
+    // 1. Embeds the manifest into test binaries via /MANIFEST:EMBED
+    // 2. Uses /MANIFEST:NO for the main binary to avoid duplicate resources
+    //    (Tauri already handles manifest embedding for the app binary)
     #[cfg(target_os = "windows")]
     {
         let manifest_path = std::path::PathBuf::from(

src-tauri/src/codex_config.rs

@@ -2,28 +2,14 @@
 use std::path::PathBuf;
 
 use crate::config::{
-    atomic_write, delete_file, sanitize_provider_name, write_json_file, write_text_file,
+    atomic_write, delete_file, get_home_dir, sanitize_provider_name, write_json_file,
+    write_text_file,
 };
 use crate::error::AppError;
 use serde_json::Value;
 use std::fs;
 use std::path::Path;
 
-/// 获取用户主目录，带回退和日志
-fn get_home_dir() -> PathBuf {
-    #[cfg(windows)]
-    if let Ok(home) = std::env::var("HOME") {
-        let trimmed = home.trim();
-        if !trimmed.is_empty() {
-            return PathBuf::from(trimmed);
-        }
-    }
-    dirs::home_dir().unwrap_or_else(|| {
-        log::warn!("无法获取用户主目录，回退到当前目录");
-        PathBuf::from(".")
-    })
-}
-
 /// 获取 Codex 配置目录路径
 pub fn get_codex_config_dir() -> PathBuf {
     if let Some(custom) = crate::settings::get_codex_override_dir() {

src-tauri/src/config.rs

@@ -6,7 +6,10 @@ use std::path::{Path, PathBuf};
 use crate::error::AppError;
 
 /// 获取用户主目录，带回退和日志
-fn get_home_dir() -> PathBuf {
+///
+/// On Windows, respects the `HOME` environment variable (if set) to support
+/// test isolation. Falls back to `dirs::home_dir()` otherwise.
+pub fn get_home_dir() -> PathBuf {
     #[cfg(windows)]
     if let Ok(home) = std::env::var("HOME") {
         let trimmed = home.trim();

src-tauri/src/gemini_config.rs

@@ -1,25 +1,10 @@
-use crate::config::write_text_file;
+use crate::config::{get_home_dir, write_text_file};
 use crate::error::AppError;
 use serde_json::Value;
 use std::collections::HashMap;
 use std::fs;
 use std::path::PathBuf;
 
-/// 获取用户主目录，带回退和日志
-fn get_home_dir() -> PathBuf {
-    #[cfg(windows)]
-    if let Ok(home) = std::env::var("HOME") {
-        let trimmed = home.trim();
-        if !trimmed.is_empty() {
-            return PathBuf::from(trimmed);
-        }
-    }
-    dirs::home_dir().unwrap_or_else(|| {
-        log::warn!("无法获取用户主目录，回退到当前目录");
-        PathBuf::from(".")
-    })
-}
-
 /// 获取 Gemini 配置目录路径（支持设置覆盖）
 pub fn get_gemini_dir() -> PathBuf {
     if let Some(custom) = crate::settings::get_gemini_override_dir() {

src-tauri/src/settings.rs

@@ -163,18 +163,11 @@ impl Default for AppSettings {
 impl AppSettings {
     fn settings_path() -> Option<PathBuf> {
         // settings.json 保留用于旧版本迁移和无数据库场景
-        #[cfg(windows)]
-        if let Ok(home) = std::env::var("HOME") {
-            let trimmed = home.trim();
-            if !trimmed.is_empty() {
-                return Some(
-                    PathBuf::from(trimmed)
-                        .join(".cc-switch")
-                        .join("settings.json"),
-                );
-            }
-        }
-        dirs::home_dir().map(|h| h.join(".cc-switch").join("settings.json"))
+        Some(
+            crate::config::get_home_dir()
+                .join(".cc-switch")
+                .join("settings.json"),
+        )
     }
 
     fn normalize_paths(&mut self) {