Fix the dead win7 context menu, flatten the selection, add a tab menu

Right-click did nothing under the win7 skin, and then swallowed the next
click. 7.css declares `position: relative` on ul[role=menu] and the `skin`
layer outranks `utilities`, so Tailwind's `.fixed` lost: [style.left/top.px]
became flow offsets from the menu's static position — the last child of the
h-screen frame — and every menu rendered below the viewport, unreachable
behind overflow:hidden. Its backdrop is a plain <div>, unmatched by 7.css, so
that stayed genuinely fixed and ate the following click. Regressed in 0ae2a62,
when the menu adopted 7.css's real markup.

Restated `position: fixed` in skinfix, scoped to a new `w7-ctx` marker so
7.css's own menus keep theirs. scripts/menu-probe.ts is the regression test:
it renders the menu at declared coordinates, pixel-scans whether it landed
there, and carries a marker-less control menu (the bug verbatim) as its own
discriminator. A resting pixel diff cannot see this class of bug.

Selection band goes flat: --w7-sel-bg/-bd (#cbe8f6/#26a0da) is what Explorer
actually painted, where 7.css reused --w7-el-grad-h, its Aero element-hover
ramp. That var is left alone — buttons and tabs still want the gloss. The
unfocused pane gets the grey idle band; the band still never disappears with
focus, it only weakens. Harness diff confirms the change touches selection
rows and nothing else, in both themes.

New workspace-tab right-click menu in both skins: New Tab, Close Tab, Close
Other Tabs, Close Tabs to the Right, Disconnect. The target id travels inside
the action string because the right-clicked tab is not necessarily the active
one. Illegal entries are disabled rather than omitted, the way Win7 greyed
out — and since 7.css's [aria-disabled] handling is CSS-only, the keyboard
paths check the flag themselves.

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

ui/src/app/skins/shadlike/context-menu.ts

@@ -51,10 +51,11 @@ const EDGE_GAP = 6; // px on purpose: a viewport-edge margin, not a UI size
               type="button"
               role="menuitem"
               [title]="item.tooltip ?? ''"
-              [class.bg-accent]="$index === activeIndex()"
+              [disabled]="!!item.disabled"
+              [class.bg-accent]="$index === activeIndex() && !item.disabled"
               (mouseenter)="activeIndex.set($index)"
               (click)="pick(item)"
-              class="flex w-full items-center gap-2 px-3 py-1 text-left text-(length:--path-font) hover:bg-accent"
+              class="flex w-full items-center gap-2 px-3 py-1 text-left text-(length:--path-font) hover:bg-accent disabled:pointer-events-none disabled:opacity-50"
             >
               <span class="w-3.5 shrink-0">
                 @if (item.checked) {
@@ -122,6 +123,8 @@ export class ContextMenu {
   }
 
   pick(item: MenuItem): void {
+    // the keyboard path never consults the disabled attribute — guard here
+    if (item.disabled) return;
     if (!item.action) return;
     const action = item.action;
     this.close();
@@ -160,14 +163,15 @@ export class ContextMenu {
     }
   }
 
-  /** Move the highlight by one selectable item, skipping separators, wrapping. */
+  /** Move the highlight by one selectable item, skipping separators and
+   *  disabled entries, wrapping. */
   private step(items: MenuItem[], delta: number): void {
     const count = items.length;
     if (!count) return;
     let index = this.activeIndex();
     for (let hops = 0; hops < count; hops++) {
       index = (index + delta + count) % count;
-      if (items[index].type !== 'separator') {
+      if (items[index].type !== 'separator' && !items[index].disabled) {
         this.activeIndex.set(index);
         return;
       }