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>

README.md

@@ -173,15 +173,33 @@ Be careful when two panels reach the same data through different mount points.
 
 ## Portability notes
 
-The codebase is platform-neutral except for two seams, both macOS-only today:
+Platform seams are isolated behind `process.platform` / `PLATFORM` branches
+marked with `PORTABILITY:` comments: editor launch (`open` / `cmd /c start` /
+`xdg-open`), app pickers, owner/group lookups, tray images, window chrome,
+shell-integration wording, drive listing, and the connections-file ACL. The
+application menu ([src/bun/menu.ts](src/bun/menu.ts)) is macOS-only for now;
+the in-app UI covers every menu action.
 
-- **External editor launch** (`launchEditor` in [src/bun/edits.ts](src/bun/edits.ts)):
-  uses macOS `open [-a app] file`. A Windows port should use
-  `cmd /c start "" [app] file`; Linux `xdg-open file` (or invoke the configured
-  editor binary directly). The `.app` picker in the `pickEditorApp` handler
-  needs the equivalent executable picker per platform.
-- **Application menu** ([src/bun/menu.ts](src/bun/menu.ts)): electrobun menus
-  are macOS-only; the in-app UI covers every menu action.
+## Windows (beta)
+
+Windows 11+ x64 is supported as a **beta** target (win-arm64 deferred). All
+electrobun APIs the app uses are implemented on Windows; known issues are
+upstream:
+
+- **HiDPI blur** ([electrobun#324](https://github.com/blackboardsh/electrobun/issues/324)):
+  WebView2 renders at 1x on scaled displays until upstream adds DPI awareness.
+- **Notifications** use legacy balloon style, not Windows toast.
+- **Unsigned binaries**: both the Setup.exe installer and the portable exe
+  trigger SmartScreen/Mark-of-the-Web warnings on first run. No Start Menu
+  entry or uninstaller (installer unpacks to `%LOCALAPPDATA%`).
+- `connections.json` is protected with an `icacls` current-user ACL instead of
+  POSIX 0600 (which is meaningless on Windows).
+
+First-Windows-boot smoke test: drives dropdown lists C:\ etc.; navigate to a
+drive root ('..' disappears); local↔remote transfers; external editor launch
+(`cmd /c start`) and the .exe picker; Show in Explorer / Recycle Bin; tray icon
+renders colored; Permissions absent on local panels; Ctrl+labels in tooltips;
+portable zip runs from any folder.
 
 ## Known issues