Windows compatibility pass (beta target)

External editor via cmd/start + exe picker; Permissions hidden for
Windows-local (chmod only flips read-only there); Explorer/Recycle Bin
wording; Ctrl vs Cmd shortcut labels; separator-aware path joins +
drive-root detection; drives list in the panel source picker; icon.ico
+ colored tray icon; icacls ACL on connections.json; README Windows
(beta) section with upstream known issues and a smoke-test checklist.
Runtime paths pending first boot on a real Windows machine.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/format.ts

@@ -42,9 +42,18 @@ export function formatEta(seconds: number): string {
   return h ? `${h}:${String(m).padStart(2, '0')}:${String(sec).padStart(2, '0')}` : mmss;
 }
 
-/** POSIX-style join for UI-composed paths (both panels use "/" on macOS + remote). */
+/**
+ * Separator-aware join for UI-composed paths: remote and POSIX-local dirs use
+ * "/", a Windows-local dir ("C:\Users\x") keeps "\" so paths stay consistent.
+ */
 export function joinPath(dir: string, name: string): string {
-  return dir.endsWith('/') ? dir + name : `${dir}/${name}`;
+  const sep = dir.includes('\\') && !dir.includes('/') ? '\\' : '/';
+  return dir.endsWith(sep) ? dir + name : `${dir}${sep}${name}`;
+}
+
+/** "/" (POSIX) or a drive root like "C:\" — nothing above to navigate to. */
+export function isRootPath(p: string): boolean {
+  return p === '/' || /^[A-Za-z]:[\\/]?$/.test(p);
 }
 
 /** 0o755 -> "rwxr-xr-x" */