fix(windows): expand compact folder chains in one click

[puppyben1]

Summary

• expand compact single-child folder chains with one action
• keep mouse and keyboard focus on the final visible directory
• preserve one-level expansion when Compact Folders is disabled
• add focused regression coverage for chains and branch stopping

Root cause

The Windows/Tauri file tree renderer could compact a folder chain only when every directory in that chain was already present in expandedPaths. The folder action loaded and expanded only one directory per click, while background preloading did not update expansion state, so each click advanced the compact path by only one segment.

Impact

With Compact Folders enabled, a single click now loads and expands through consecutive single-child directories until it reaches files, an empty directory, or a branch. Local, WSL, and SSH workspaces share the same provider path.

Validation

• focused regression tests: 2 passed
• TypeScript typecheck passed
• lint passed for changed files
• production frontend build passed
• Windows release executable built successfully
• manually verified on Windows: compact folder expansion behaves as expected

The full existing frontend suite reports unrelated failures in icon inventory and Git API mock/export tests; the new directory-tree tests pass.

Closes #151