fix(installer): improve Windows compatibility for shell detection and paths

Closes #461

src/shared/command-executor/shell-path.test.ts

@@ -0,0 +1,39 @@
+import { afterEach, beforeEach, describe, expect, test } from "bun:test"
+import { findBashPath } from "./shell-path"
+
+describe("shell-path", () => {
+  let originalPlatform: NodeJS.Platform
+  let originalComspec: string | undefined
+
+  beforeEach(() => {
+    originalPlatform = process.platform
+    originalComspec = process.env.COMSPEC
+  })
+
+  afterEach(() => {
+    Object.defineProperty(process, "platform", { value: originalPlatform })
+    if (originalComspec !== undefined) {
+      process.env.COMSPEC = originalComspec
+      return
+    }
+    delete process.env.COMSPEC
+  })
+
+  test("#given Windows platform with COMSPEC #when findBashPath is called #then returns COMSPEC path", () => {
+    Object.defineProperty(process, "platform", { value: "win32" })
+    process.env.COMSPEC = "C:\\Windows\\System32\\cmd.exe"
+
+    const result = findBashPath()
+
+    expect(result).toBe("C:\\Windows\\System32\\cmd.exe")
+  })
+
+  test("#given Windows platform without COMSPEC #when findBashPath is called #then returns default cmd path", () => {
+    Object.defineProperty(process, "platform", { value: "win32" })
+    delete process.env.COMSPEC
+
+    const result = findBashPath()
+
+    expect(result).toBe("C:\\Windows\\System32\\cmd.exe")
+  })
+})