Fix Windows workspace cache setup

[rshabhsinha]

Summary

Fixes a Windows startup failure in pcb build / pcb layout when creating <workspace>/.pcb/cache.

Windows can reject directory symlink creation with os error 1314 unless Developer Mode or elevated privileges are enabled. This keeps the existing symlink path when available, and falls back to an NTFS junction for normal non-admin Windows users.

Also handles replacing stale .pcb/cache junctions safely.

Tests

• cargo fmt --check
• cargo check -p pcb-zen
• cargo test -p pcb-zen --lib

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Note

Medium Risk
Moderate risk because it changes filesystem link creation/removal behavior for the workspace cache on Windows, which could affect startup and path stability if edge cases are missed.

Overview
Fixes Windows failures creating <workspace>/.pcb/cache by falling back from directory symlinks to NTFS junctions when symlink creation is denied (e.g., os error 1314).

Refactors ensure_workspace_cache_symlink to detect whether the existing cache entry already targets ~/.pcb/cache (symlink or junction), safely replace stale entries, and only add the junction dependency on Windows. Updates the changelog to document the fix.

^{Reviewed by Cursor Bugbot for commit 88e9fe2. Configure here.}