wire the output dock into the layout — toggle, tabs, persistence (T-54)

The D-87 bottom dock, end to end. New Slots.dock in the classic preset
(hidden by default); RootLayout renders it full-width above the status bar
when open, capped at half the window so Claude stays largest (the D-47
amendment). LogRing now lives on KernelServices (boot tees the kernel logger
into it; main.dart also tees the IPC/MCP logger), so the dock shows logs from
every subsystem.

OutputExtension contributes the Output tab, the merged health/toggle
status-bar widget (green check when clean, warn/error counts otherwise) that
replaces the old ipc-status item, and the dock.toggle command (Ctrl+J).
Problems moves out of the sidebar into the dock. open/height persist per
workspace via the default-layout extension.

Drag-resize of the dock height is deferred (DragResizeHandle needs a dock
sign case); height is the persisted default for now. Boot verified via
testmode; full suite green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/kernel/src/panels/layout_preset.dart

@@ -32,6 +32,14 @@ LayoutPresetContribution classicPreset() => const LayoutPresetContribution(
           minSize: 220,
           maxSize: 1000,
         ),
+        LayoutSlot(
+          slot: Slots.dock,
+          position: SlotPosition.bottom,
+          defaultSize: 200,
+          minSize: 100,
+          maxSize: 600,
+          visible: false,
+        ),
         LayoutSlot(
           slot: Slots.statusbar,
           position: SlotPosition.bottom,

lib/kernel/src/panels/slot_id.dart

@@ -22,6 +22,10 @@ abstract class Slots {
   static const workspace = SlotId('workspace');
   static const contextPanel = SlotId('context');
   static const statusbar = SlotId('statusbar');
+
+  /// Bottom output dock — read-only logs + problems (T-54 / D-87). Toggled;
+  /// hidden by default.
+  static const dock = SlotId('dock');
   static const toolbar = SlotId('toolbar.main');
   static const commandPalette = SlotId('commandPalette');
   static const tray = SlotId('tray');