Give a dashboard the panel's own size, and put the dots on its grid

A dashboard now carries the canvas it is drawn for (canvas_width /
canvas_height, presets plus two numbers in the settings panel). Editor and
wall panel render that surface at its true pixel size and scale it to fit,
so a side panel opening changes only the scale — never the arrangement
being made. With the width and column count known the dot pitch is exact,
(width + gap) / columns by row height + gap, so a dot sits where every
widget corner snaps. The wall panel shows no dots.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H7LwYgJfpkbLCTeiAf8U4A

frontend/src/client/schemas.gen.ts

@@ -218,6 +218,20 @@ export const DashboardDef_InputSchema = {
             title: 'Columns',
             default: 12
         },
+        canvas_width: {
+            type: 'integer',
+            maximum: 7680,
+            minimum: 0,
+            title: 'Canvas Width',
+            default: 1920
+        },
+        canvas_height: {
+            type: 'integer',
+            maximum: 4320,
+            minimum: 0,
+            title: 'Canvas Height',
+            default: 1080
+        },
         pages: {
             items: {
                 '$ref': '#/components/schemas/PageDef-Input'
@@ -255,6 +269,20 @@ export const DashboardDef_OutputSchema = {
             title: 'Columns',
             default: 12
         },
+        canvas_width: {
+            type: 'integer',
+            maximum: 7680,
+            minimum: 0,
+            title: 'Canvas Width',
+            default: 1920
+        },
+        canvas_height: {
+            type: 'integer',
+            maximum: 4320,
+            minimum: 0,
+            title: 'Canvas Height',
+            default: 1080
+        },
         pages: {
             items: {
                 '$ref': '#/components/schemas/PageDef-Output'

frontend/src/client/types.gen.ts

@@ -83,6 +83,8 @@ export type DashboardDef_Input = {
     name: string;
     title?: string;
     columns?: number;
+    canvas_width?: number;
+    canvas_height?: number;
     pages?: Array<PageDef_Input>;
     version?: number;
 };
@@ -94,6 +96,8 @@ export type DashboardDef_Output = {
     name: string;
     title?: string;
     columns?: number;
+    canvas_width?: number;
+    canvas_height?: number;
     pages?: Array<PageDef_Output>;
     version?: number;
 };