Move settings into a standalone Settings window

The tab-bar popover had outgrown itself. Settings now open in their own
native window (a fourth window kind, built like the connection manager but
not modal): a sidebar with Appearance, Transfers, Editor, File list and
About, holding every popover row plus the visible-columns choice. Each
control is an ordinary settings save, so the other windows follow live
while it stays open.

The gear button in the tab bar, Ctrl+, and the macOS app menu's
"Settings..." (Cmd+,) open it. On macOS Cmd+W arrives as the main window's
close-tab menu action, so bun closes the focused Settings window first
instead of a main-window tab.

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

docs/architecture.md

@@ -30,8 +30,8 @@ Each `BrowserWindow` MUST receive its own `defineRPC(...)` instance: binding a
 BrowserView calls `rpc.setTransport(...)`, so a shared instance would have its
 transport stolen by the most recent window. `createAppRPC` (main),
 `createEditorRPC` (per editor window, hooks close over that window's record),
-`createManagerRPC` (the single manager window). `rpc.send.*` on an instance
-targets exactly its own webview.
+`createManagerRPC` (the single manager window), `createSettingsRPC` (the single
+Settings window). `rpc.send.*` on an instance targets exactly its own webview.
 
 ### The `events` late-binding pattern
 
@@ -39,15 +39,15 @@ targets exactly its own webview.
 exist until after construction). `AppDeps.events` is a mutable object of
 no-op functions, reassigned in `src/bun/index.ts` after everything exists:
 `sessionClosed`, `connectionsChanged`, `openEditor`, `settingsChanged`,
-`openConnectionManager`, `showAbout`.
+`openConnectionManager`, `openSettings`, `showAbout`.
 
 ## Window kinds
 
 `src/bun/windows.ts` — `buildPreload(mode, settings, ctx?)` injects
-`__APP_PLATFORM`, `__APP_MODE` (`main|editor|manager`), `__APP_CTX` before any
-page script, plus the persisted theme attributes and interface scale so the
-first paint is already right. `ui/src/main.ts` picks the root component from
-`APP_MODE`; all three roots use selector `app-root` (index.html hosts only that
+`__APP_PLATFORM`, `__APP_MODE` (`main|editor|manager|settings`), `__APP_CTX`
+before any page script, plus the persisted theme attributes and interface
+scale so the first paint is already right. `ui/src/main.ts` picks the root component from
+`APP_MODE`; all four roots use selector `app-root` (index.html hosts only that
 tag). `chromeOptions()` is the ONLY place the native frame is decided, spread by
 the main window and `openSecondaryWindow`: macOS `hiddenInset` +
 `trafficLightOffset {x:12,y:13}` (the UI renders an `h-10 pl-24` drag-region
@@ -103,6 +103,20 @@ main's `ConnectionsService` reloads; a reload-retry in `App.findConnection`
 covers the save→connect race. `setAlwaysOnTop` is deliberately NOT used (it
 would float over editor windows).
 
+### Settings window (`src/bun/settings-window.ts` + `ui/src/app/skins/shadlike/settings-window/`)
+
+Single instance, centered over main, **not modal**: every control is a plain
+`SettingsService` setter, so each edit is an ordinary save that bun
+rebroadcasts — the other windows follow live while it stays open. Opened by
+the tab-bar gear and Ctrl+, (`openSettings` from main) and, on macOS, the app
+menu's "Settings…" (⌘,, which the menu intercepts first). Its RPC serves only
+`getSettings`/`saveSettings`/`pickEditorApp`/`showAbout`. ⌘W reaches bun as
+the main window's `close-tab` menu action, so bun checks the Settings window's
+focus FIRST and closes it (see gotchas). Sidebar sections: Appearance,
+Transfers, Editor, File list (visible columns — the column-header right-click
+menu toggles the same setting), About (opens the native About box). The
+native title is `options.title`, retitled on a locale switch.
+
 ## Bun modules
 
 - `fs/provider.ts` — `FileSystemProvider` interface: uniform local/SFTP ops +
@@ -152,8 +166,9 @@ would float over editor windows).
   atomic tmp+rename, 0600 + win32 `icacls` ACL. `store/settings.ts` — defaults
   spread-merge on load, so NEW SETTINGS KEYS need no backend change.
 - `menu.ts` — macOS-only app menu, rebuilt on every connections change (the
-  Connect submenu mirrors the store). ⌘W is intercepted by the menu, so bun
-  routes `close-tab` to the focused editor window first. Labels go through
+  Connect submenu mirrors the store; "Settings…" carries ⌘,). ⌘W is intercepted
+  by the menu, so bun routes `close-tab` to a focused Settings or editor window
+  first. Labels go through
   backend `i18n.t` and the menu is rebuilt on a locale change too.
 - `i18n.ts` — backend translator (native menus + thrown error messages, which
   no Angular service can reach). `setLocale(setting)` caches the resolved
@@ -175,7 +190,7 @@ would float over editor windows).
 ui/src/app/
   core/            app.config.ts, icons.ts, platform.ts, format.ts, file-icons.ts,
                    metrics.ts and every *.service.ts — the non-visual layer
-  skins/shadlike/  the component tree: three window roots (SHAD_ROOTS barrel,
+  skins/shadlike/  the component tree: four window roots (SHAD_ROOTS barrel,
                    picked by main.ts), dialogs, context menu
 ```
 
@@ -220,8 +235,9 @@ component; tokens → `ui/src/styles.css`.
   (`applyTheme/DarkTone/Accent` set `data-*` attributes on `<html>`;
   `applyUiScale` sets its inline `font-size`); `applyAll` also serves the
   `settingsChanged` broadcast, so every window follows a save made in any
-  other. All three window RPCs serve `saveSettings` (editor and manager windows
-  save too — the scale shortcuts); bun's `settingsSaved()` in index.ts runs the
+  other. Every window RPC serves `saveSettings` (editor and manager windows
+  save too — the scale shortcuts — and the Settings window is nothing but
+  saves); bun's `settingsSaved()` in index.ts runs the
   side effects once and rebroadcasts to every window **except the sender**, so
   there is no echo to fight a held Cmd+. `applyAll` never persists. New setting
   = five touches here + types.ts (backend merges automatically).
@@ -316,7 +332,7 @@ pixel-identical to the old neutral hover. **Interface scale** (`settings.uiScale
 `html { font-size: 16px * scale }`, and since EVERY size in the app is rem
 (panel tokens like `--row-h`, all Tailwind utilities, ng-icon sizes), the
 whole UI scales, chrome included.
-Driven by the tab-bar stepper, Ctrl/Cmd +/−/0, and preload-baked for a
+Driven by the Settings window's stepper, Ctrl/Cmd +/−/0, and preload-baked for a
 flash-free first paint. It replaced the 3-tier `data-text` axis; the store
 migrates old `textSize` values. TS that measures rem-sized CSS converts through
 `@core/metrics` `remPx()` — never an assumed 16.