fix: Windows auto-update path detection and install function support (#404)

* fix: Windows auto-update path detection and add install function support

- Fix Windows path inconsistency: check ~/.config first, then %APPDATA%
- Add actual update installation via runBunInstall when autoUpdate=true
- Check both Windows config locations for comprehensive detection

Closes #402

* fix: address review feedback on error logging and message clarity

- Update misleading log message to clarify fallback behavior
- Serialize error object before logging to prevent {} serialization

---------

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/hooks/auto-update-checker/constants.ts

@@ -1,5 +1,6 @@
 import * as path from "node:path"
 import * as os from "node:os"
+import * as fs from "node:fs"
 
 export const PACKAGE_NAME = "oh-my-opencode"
 export const NPM_REGISTRY_URL = `https://registry.npmjs.org/-/package/${PACKAGE_NAME}/dist-tags`
@@ -28,14 +29,36 @@ export const INSTALLED_PACKAGE_JSON = path.join(
 
 /**
  * OpenCode config file locations (priority order)
+ * On Windows, checks ~/.config first (cross-platform), then %APPDATA% (fallback)
+ * This matches shared/config-path.ts behavior for consistency
  */
 function getUserConfigDir(): string {
   if (process.platform === "win32") {
-    return process.env.APPDATA ?? path.join(os.homedir(), "AppData", "Roaming")
+    const crossPlatformDir = path.join(os.homedir(), ".config")
+    const appdataDir = process.env.APPDATA ?? path.join(os.homedir(), "AppData", "Roaming")
+    
+    // Check cross-platform path first (~/.config)
+    const crossPlatformConfig = path.join(crossPlatformDir, "opencode", "opencode.json")
+    const crossPlatformConfigJsonc = path.join(crossPlatformDir, "opencode", "opencode.jsonc")
+    
+    if (fs.existsSync(crossPlatformConfig) || fs.existsSync(crossPlatformConfigJsonc)) {
+      return crossPlatformDir
+    }
+    
+    // Fall back to %APPDATA%
+    return appdataDir
   }
   return process.env.XDG_CONFIG_HOME ?? path.join(os.homedir(), ".config")
 }
 
+/**
+ * Get the Windows-specific APPDATA directory (for fallback checks)
+ */
+export function getWindowsAppdataDir(): string | null {
+  if (process.platform !== "win32") return null
+  return process.env.APPDATA ?? path.join(os.homedir(), "AppData", "Roaming")
+}
+
 export const USER_CONFIG_DIR = getUserConfigDir()
 export const USER_OPENCODE_CONFIG = path.join(USER_CONFIG_DIR, "opencode", "opencode.json")
 export const USER_OPENCODE_CONFIG_JSONC = path.join(USER_CONFIG_DIR, "opencode", "opencode.jsonc")