refactor(layouts): simplify to global config + preserve windows + add UI dropdown

Simplified layout system based on user feedback:

**1. Global Layout Config (Simpler)**
- Moved layoutConfig from per-workspace to global state
- One configuration applies to all workspaces (easier to understand)
- Updated state migration v8→v9 to move config to global level
- Updated WorkspaceSettings UI to edit global config
- Renamed updateWorkspaceLayoutConfig → updateLayoutConfig

**2. Preserve Extra Windows (Fixed Bug)**
- Fixed applyPresetToLayout to keep windows beyond preset slots
- When applying 4-window grid to 6 windows, windows 5-6 are preserved
- Extra windows stacked vertically on right side (70/30 split)
- No more window loss when applying presets

**3. Layout Dropdown in TabBar (Better UX)**
- Added dropdown menu next to workspace tabs
- Shows all available presets with icons (Grid2X2, Columns2, Split)
- Displays window requirements and availability
- Disables presets that need more windows than available
- One-click preset application with toast feedback
- More accessible than /layout command

All tests passing (457 passed). State migration handles v6→v7→v8→v9 correctly.

Generated with [Claude Code](https://claude.com/claude-code)

src/core/logic.test.ts

@@ -131,16 +131,16 @@ describe("findLowestAvailableWorkspaceNumber", () => {
 describe("addWindow", () => {
   // Helper to create minimal test state
   const createTestState = (layoutConfig: LayoutConfig, existingLayout: MosaicNode<string> | null = null): GrimoireState => ({
-    __version: 8,
+    __version: 9,
     windows: {},
     activeWorkspaceId: "test-workspace",
+    layoutConfig, // Global layout config (not per-workspace)
     workspaces: {
       "test-workspace": {
         id: "test-workspace",
         number: 1,
         windowIds: [],
         layout: existingLayout,
-        layoutConfig,
       },
     },
   });

src/core/logic.ts

@@ -76,8 +76,8 @@ export const addWindow = (
     commandString: payload.commandString,
   };
 
-  // Insert window using workspace layout configuration
-  const newLayout = insertWindow(ws.layout, newWindowId, ws.layoutConfig);
+  // Insert window using global layout configuration
+  const newLayout = insertWindow(ws.layout, newWindowId, state.layoutConfig);
 
   return {
     ...state,
@@ -347,30 +347,18 @@ export const updateWindow = (
 };
 
 /**
- * Updates the layout configuration for a workspace.
- * Controls how new windows are inserted into the workspace layout.
+ * Updates the global layout configuration.
+ * Controls how new windows are inserted into all workspaces.
  */
-export const updateWorkspaceLayoutConfig = (
+export const updateLayoutConfig = (
   state: GrimoireState,
-  workspaceId: string,
-  layoutConfig: Partial<GrimoireState["workspaces"][string]["layoutConfig"]>,
+  layoutConfig: Partial<GrimoireState["layoutConfig"]>,
 ): GrimoireState => {
-  const workspace = state.workspaces[workspaceId];
-  if (!workspace) {
-    return state; // Workspace doesn't exist, return unchanged
-  }
-
   return {
     ...state,
-    workspaces: {
-      ...state.workspaces,
-      [workspaceId]: {
-        ...workspace,
-        layoutConfig: {
-          ...workspace.layoutConfig,
-          ...layoutConfig,
-        },
-      },
+    layoutConfig: {
+      ...state.layoutConfig,
+      ...layoutConfig,
     },
   };
 };

src/core/state.ts

@@ -18,14 +18,14 @@ const initialState: GrimoireState = {
       number: 1,
       windowIds: [],
       layout: null,
-      layoutConfig: {
-        insertionMode: "smart", // Smart auto-balancing by default
-        splitPercentage: 50, // Equal split
-        insertionPosition: "second", // New windows on right/bottom
-        autoPreset: undefined, // No preset maintenance
-      },
     },
   },
+  layoutConfig: {
+    insertionMode: "smart", // Smart auto-balancing by default
+    splitPercentage: 50, // Equal split
+    insertionPosition: "second", // New windows on right/bottom
+    autoPreset: undefined, // No preset maintenance
+  },
 };
 
 // Custom storage with error handling and migrations
@@ -229,14 +229,9 @@ export const useGrimoire = () => {
     [setState],
   );
 
-  const updateWorkspaceLayoutConfig = useCallback(
-    (
-      workspaceId: string,
-      layoutConfig: Partial<GrimoireState["workspaces"][string]["layoutConfig"]>,
-    ) =>
-      setState((prev) =>
-        Logic.updateWorkspaceLayoutConfig(prev, workspaceId, layoutConfig),
-      ),
+  const updateLayoutConfig = useCallback(
+    (layoutConfig: Partial<GrimoireState["layoutConfig"]>) =>
+      setState((prev) => Logic.updateLayoutConfig(prev, layoutConfig)),
     [setState],
   );
 
@@ -259,7 +254,7 @@ export const useGrimoire = () => {
     setActiveWorkspace,
     setActiveAccount,
     setActiveAccountRelays,
-    updateWorkspaceLayoutConfig,
+    updateLayoutConfig,
     applyPresetLayout,
   };
 };