feat: add automatic mobile board layout

apps/docs/docs/management/boards/index.mdx

@@ -90,11 +90,12 @@ Homarr will fall back to the Homarr logo if nothing is set.
 
 ### Layout
 
-In this section you can configure the different responsive layouts.
-Homarr selects a layout from the screen width, then scales its complete fixed-size canvas uniformly.
+In this section you can configure the different responsive layouts. Homarr selects the layout with the highest breakpoint that is not wider than the current screen, then scales its complete fixed-size canvas uniformly.
 
 ![](./img/layout-settings.png)
 
+Every board has two protected layouts:
+
 Every `1 × 1` tile has a `200 × 200` logical-pixel content area.
 The `24` logical-pixel gap between tiles is separate from that size.
 A `2 × 1` tile therefore contains two fixed cell widths plus the gap between them.
@@ -103,28 +104,31 @@ When fitting below 100%, Homarr keeps widget typography and control density at t
 On larger canvases, the complete board grows together like browser zoom.
 The complete canvas always fits the available width and never adds horizontal board scrolling.
 
-The position and size of every item are independent in each responsive layout.
-Moving or resizing an item in one layout does not change any other layout.
-When adding a new layout, its initial positions and sizes are generated from the column count.
-New items use their widget's default grid size, while a new Container starts at a useful `4 × 3` size when the layout has enough columns.
-Both are placed in the first available position.
+- **Mobile** starts at `0px` and uses three columns on new boards.
+- **Base** is the widest layout and starts at `768px` on new boards.
+
+Mobile and Base can be renamed and their column counts can be changed, but they cannot be removed. Mobile has no fixed rails; rail configuration is available only on Base and custom layouts. You can add removable custom layouts between their breakpoints.
+
+Each layout stores independent positions and sizes. Moving or resizing a widget while editing Mobile does not move it in Base or any custom layout. New custom layouts are generated from Base and scaled to their selected column count.
+
+Use **Reset from Base** on Mobile or a custom layout to replace all of its positions and sizes with a newly generated version of Base. The layout's name, breakpoint, and column count are kept.
 
 The canvas is at least one window tall, even when it is empty.
 Its left and right edges are hard drag boundaries, while its bottom edge extends automatically as a tile is dragged or resized downward.
 Nested Containers keep their own resizable bounds.
+New items use their widget's default size and new Containers use a useful `4 × 3` size when space allows.
 
 #### Name
 
-The name of the layout can be chosen freely. It is only used for management and will not be visible on the board.
+The name of the layout can be chosen freely. It is only used for management and is not displayed on the board.
 
 #### Column count
 
-Total number of columns for this layout.
-When changed, Homarr moves items into the next available positions without overlap.
+The total number of columns in the layout. Changing it projects the saved positions and sizes into the new grid width without overlap.
 
 #### Fixed rails
 
-Each responsive layout can enable a fixed left rail, a fixed right rail, or both.
+Base and custom responsive layouts can enable a fixed left rail, a fixed right rail, or both. Mobile has no fixed rails.
 Set a rail width to zero to disable it for that layout.
 Choose a width from one to three columns with the three-step slider.
 The preview shows how much space remains for the main canvas.
@@ -139,8 +143,7 @@ Apps, widgets, and Containers inside them still use the same fixed `200 × 200`
 
 #### Breakpoint
 
-Minimum width of the screen where the layout will be used.
-Once the minimum of the next layout is reached, the layout will change.
+The minimum screen width where the layout is used. Mobile is fixed at `0px`. Custom breakpoints must be unique and sit between Mobile and Base. Base must remain the highest breakpoint.
 
 #### View and edit modes
 
@@ -165,6 +168,10 @@ The **Move / resize item** action in the edit menu remains available for precise
 
 #### Preview
 
+Layout Settings shows a lightweight structural preview for every layout, including saved spans, Containers, widget labels, and app icons. The canvas width represents the screen range where that layout is active.
+
+Choose **Edit layout** to open the real board editor at that representative width on desktop. Save returns to Layout Settings. Cancel discards the local changes. On phones and tablets, the normal board editor continues to use the layout selected by the device width.
+
 <img src={layoutSmallImage} height={256} />
 <img src={layoutMediumImage} height={256} />
 <img src={layoutLargeImage} height={256} />