fix: skip bash-dependent tests on Windows, fix platform-aware assertions

- Skip worktree test suite on Windows (uses bash shell syntax)
- Skip ~ home-root directory test on Windows
- Make findExecutable mock assertions platform-aware (which vs where.exe)
- Use nonexistent binary name for not-found test case

packages/server/src/utils/worktree.test.ts

@@ -26,7 +26,7 @@ import { dirname, join } from "path";
 import { tmpdir } from "os";
 import net from "node:net";
 
-describe("createWorktree", () => {
+describe.skipIf(process.platform === "win32")("createWorktree", () => {
   let tempDir: string;
   let repoDir: string;
   let paseoHome: string;