Tray: Replace the notch with a controls strip on the dock's edge

[mmtr]

Proposed Changes

• The notch is gone. A tray takes its place: a strip that wraps the bottom dock and extends above it, carrying the site assistant's front door and Exit OpenStation.
• The assistant gets a visible way in. Core's command-palette button is hijacked to open it, but the admin bar that button lives in is hidden by default, so the only entry point was the keyboard. The tray shows the site mark and the ⌘K / Ctrl+K chord.
• Exit OpenStation moves off the dock rail into the tray.
• On a left- or right-placed rail there is no tray, so the same two controls become tiles instead: the assistant leads the rail, the exit closes it as before.
• SystemDockItem.navKind gains 'core', the only kind that sorts ahead of Dashboard. Additive, so existing values are unaffected.

Unified	Split

Why are these changes being made?

The assistant had no visible entry point at all, and the notch it lived on was a second piece of floating chrome on a desktop whose whole point is not having any. Drawn as the dock's own edge, thickened until the controls fit inside it, it belongs to something already on screen.

Exit OpenStation was the other half. On the rail it had to be drawn as an exception to every rule the dock had (its own gap, a ring instead of a plate, a hover that leaned the other way) because the dock is a list of things you open and close and the exit does neither.

Testing Instructions

1. Open OpenStation with the dock at the bottom. Make sure a strip sits on the dock's top edge, the same width as the dock, holding the site-mark glyph with ⌘K beside it and an exit glyph at the trailing end.
2. Click the site mark. Make sure the assistant opens. Press ⌘K (Ctrl+K on Windows/Linux) and make sure it opens the same surface.
3. Click the exit glyph. Make sure you land back in the classic admin, then return to OpenStation.
4. Hover each control. Make sure a label appears above the strip reading "Open site assistant" and "Exit OpenStation", and that neither is clipped by the strip's rounded corners.
5. Hover the exit control and look at the strip's trailing corner. Make sure the hover fill follows the rounded corner instead of spilling past it.
6. Open any wp-admin window and move it so it sits under the strip. Make sure the strip stays dark and its glyphs stay legible against the light window.
7. Switch to the Legacy desktop theme (OpenStation Preferences > Appearance > Desktop theme). Make sure the strip follows Legacy's dock colours and its glyphs are still legible.
8. Maximize a window. Make sure it stops below the strip rather than sliding under it.
9. OpenStation Preferences > Appearance > Desktop layout, move the dock to the left. Make sure the strip is gone, the site assistant is the first item on the rail as a full-width band with its shortcut, and Exit OpenStation is the last tile with its ring.
10. Click the assistant band on the rail, then the exit tile. Make sure both still do what they say.
11. Switch to the Split layout. Make sure the sidebar has no assistant band (the tray on the bottom dock carries it) and that its first menu tile is not flush against the top edge.
12. Move the dock back to the bottom. Make sure the strip returns and the two rail tiles are gone.
13. Activate or deactivate a plugin that adds an admin menu, so the dock changes width. Make sure the strip stays exactly as wide as the dock and centred on it.
14. Enter the window overview (double-tap the desktop or the Overview tile). Make sure the strip fades out with the rest of the chrome.