Stop two docstrings describing a schema that is gone

Pages and sections left in 7ff29ca. DashboardView still promised SectionDef
stayed and that the editor wrote back into the first section; the mosaic
still said "the first page's widgets". Comments only — the code was right.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K1moruzue2kTJd3uVisgNk

frontend/src/components/Common/DashboardMosaic.tsx

@@ -65,10 +65,7 @@ type Block = {
   h: number
 }
 
-/**
- * The first page's widgets as one grid.
- *
- */
+/** The dashboard's widgets as one grid. */
 function blocksOf(dashboard: DashboardDef_Output): {
   blocks: Block[]
   rows: number