Give both summaries a modified time, and the dashboard list a footprint

Home's "recently modified" order was a proxy — drafts first, then the
version counter, then the name. Both summaries now carry `updated_at`,
read as the mtime of the working copy: every write in the store commits
immediately, so a file's mtime is its commit time, and `git log -1 --
<path>` costs ~990ms across this instance's 15 documents (it walks the
history back to the last commit touching each one, so it is slowest for
the stalest) against ~1.8ms for the stats. No cache needed.

`DashboardSummary` also carries `footprint`: each widget as its type plus
the placement a panel resolves, which is the whole of what the mosaic
draws. That drops the document fetch per tile and with it the cap of
eight, past which tiles showed a name and nothing else. Verified against
this instance's 8 dashboards: the blocks are identical to what the old
client-side derivation produced.

frontend/src/client/schemas.gen.ts

@@ -575,6 +575,30 @@ export const DashboardSummarySchema = {
             type: 'integer',
             title: 'Version',
             default: 1
+        },
+        columns: {
+            type: 'integer',
+            title: 'Columns',
+            default: 12
+        },
+        footprint: {
+            items: {
+                '$ref': '#/components/schemas/WidgetFootprint'
+            },
+            type: 'array',
+            title: 'Footprint'
+        },
+        updated_at: {
+            anyOf: [
+                {
+                    type: 'string',
+                    format: 'date-time'
+                },
+                {
+                    type: 'null'
+                }
+            ],
+            title: 'Updated At'
         }
     },
     type: 'object',
@@ -1303,6 +1327,18 @@ export const FlowSummarySchema = {
             type: 'integer',
             title: 'Version',
             default: 1
+        },
+        updated_at: {
+            anyOf: [
+                {
+                    type: 'string',
+                    format: 'date-time'
+                },
+                {
+                    type: 'null'
+                }
+            ],
+            title: 'Updated At'
         }
     },
     type: 'object',
@@ -3834,6 +3870,45 @@ The first two are a \`\`list\`\` message, the third a \`\`str\`\`, which is what
 \`\`COLOR_DTYPES\`\` records and the check below holds a binding to.`
 } as const;
 
+export const WidgetFootprintSchema = {
+    properties: {
+        x: {
+            type: 'integer',
+            title: 'X',
+            default: 0
+        },
+        y: {
+            type: 'integer',
+            title: 'Y',
+            default: 0
+        },
+        w: {
+            type: 'integer',
+            title: 'W',
+            default: 3
+        },
+        h: {
+            type: 'integer',
+            title: 'H',
+            default: 2
+        },
+        type: {
+            type: 'string',
+            enum: ['stat', 'gauge', 'chart', 'markdown', 'agenda', 'notification', 'bar', 'icon', 'forecast', 'clock', 'media', 'player', 'embed', 'button', 'switch', 'slider', 'input', 'dropdown', 'color'],
+            title: 'Type'
+        }
+    },
+    type: 'object',
+    required: ['type'],
+    title: 'WidgetFootprint',
+    description: `A widget reduced to the shape it draws: what it is, and where it sits.
+
+The whole of what sketching a dashboard's outline needs — a mosaic tile
+shades a block by kind and puts it in the grid, and reads nothing else. So
+no id (the drawing has no use for one), no title, no config, and one
+placement rather than the layout's breakpoint per screen size.`
+} as const;
+
 export const WorkerInfoSchema = {
     properties: {
         name: {

frontend/src/client/types.gen.ts

@@ -158,6 +158,9 @@ export type DashboardSummary = {
     widget_count?: number;
     has_draft?: boolean;
     version?: number;
+    columns?: number;
+    footprint?: Array<WidgetFootprint>;
+    updated_at?: (string | null);
 };
 
 export type DeadLetter = {
@@ -408,6 +411,7 @@ export type FlowSummary = {
     paused?: boolean;
     quarantined?: boolean;
     version?: number;
+    updated_at?: (string | null);
 };
 
 export type fluksio__api__routes__dashboards__PublishRequest = {
@@ -1314,6 +1318,22 @@ export type WidgetDef = {
 
 export type type = 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color';
 
+/**
+ * A widget reduced to the shape it draws: what it is, and where it sits.
+ *
+ * The whole of what sketching a dashboard's outline needs — a mosaic tile
+ * shades a block by kind and puts it in the grid, and reads nothing else. So
+ * no id (the drawing has no use for one), no title, no config, and one
+ * placement rather than the layout's breakpoint per screen size.
+ */
+export type WidgetFootprint = {
+    x?: number;
+    y?: number;
+    w?: number;
+    h?: number;
+    type: 'stat' | 'gauge' | 'chart' | 'markdown' | 'agenda' | 'notification' | 'bar' | 'icon' | 'forecast' | 'clock' | 'media' | 'player' | 'embed' | 'button' | 'switch' | 'slider' | 'input' | 'dropdown' | 'color';
+};
+
 export type WorkerInfo = {
     name: string;
     labels?: Array<(string)>;