Skin is a launch-time choice; stop applying it to a live window

Switching Modern -> Win7 at runtime broke the UI. SettingsService.applySkin
toggled the `.win7` class the moment the setting changed — harmless when there
was one component tree, and a broken window as soon as there were two. The tree
is bootstrapped once from the preload-baked __APP_SKIN, so the live flip painted
7.css onto shadlike markup that has no .window.glass, no .title-bar, no
menu[role=tablist] and no <table> ListView. The CSS landed on a tree that cannot
receive it.

A reload would not have helped, and neither would anything short of a restart:

- The preload is a persistent WebKitUserScript injected at DOCUMENT_START, so
  its string is frozen at webview construction — loadURL() re-runs it with the
  OLD __APP_SKIN. updatePreloadScriptToWebView exists in the FFI but is
  reachable only from electrobun's internal <electrobun-webview> handler.
- titleBarStyle/transparent have no setters; a live window cannot be re-framed.
  win7 -> modern is the dangerous direction — the modern tree draws no title
  bar, so it would land in a frameless transparent window with no way to move,
  minimize or close it.
- Recreating the main window is also out: exitOnLastWindowClosed is true, the
  main rpc is captured by six push closures, the tray captures `win`, and
  listeners cannot be removed.

So: applySkin is deleted outright, from setSkin AND from applyAll — the latter
matters independently, since applyAll runs on the settingsChanged push and was
therefore breaking every open editor and manager window too. Clicking a skin now
only persists it.

Also fixed a second leak found while tracing this: manager-window and
editor-windows build from `currentSettings()`, the LIVE snapshot, so a window
opened after a pending change would boot the new tree and frame while main still
ran the old one. `initSessionSkin` now freezes the skin at startup before any
window exists, and buildPreload/chromeOptions read that pinned value —
chromeOptions loses its parameter so no call site can get it wrong.

The options row shows the saved value as pending (skinPending() compares
settings.skin() against APP_SKIN) with the hint retexted in all 7 locales; it
said "Reopen the window to change its frame", which described the deleted
design.

Verified: tsc + build:ui clean; both skins boot correctly from a persisted
setting (win7 frameless, modern with the native frame). The live flip is now
impossible by construction, which is the check that matters here — the UI bundle
contains no classList write for win7 at all, the only writer is buildPreload,
and sessionSkin has exactly one assignment site.

Not verified: the click itself and the pending hint appearing, which need an
interaction pass — no window automation is available here. Both are present in
the built bundle.

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

ui/src/app/skins/7like/7like.css

@@ -1,6 +1,7 @@
 /* The SCOPED 7.css build: postcss-prefix-selector rewrote every selector to
    `.win7` (root rules) or `.win7 <sel>` (the rest), so the whole framework is
-   inert until SettingsService.applySkin puts that class on <html>. All 61
+   inert until the `.win7` class is on <html> — written once by buildPreload
+   for the skin this window booted, and never changed after. All 61
    icons are data URIs, so nothing needs copying into assets — and NOT the
    `7.inline.css` build, which flattens away the --w7-* vars the dark palette
    below depends on. The deep path is required: 7.css ships no `exports` map
@@ -9,7 +10,7 @@
 @import "7.css/dist/7.scoped.css" layer(skin);
 
 /* ==========================================================================
-   Windows 7 skin — SettingsService.applySkin puts `.win7` on <html>
+   Windows 7 skin — buildPreload puts `.win7` on <html> at first paint
    ==========================================================================
 
    Three tiers, and the split matters: