feat(board): canonical board definition and BoardView (T2)

Encode the board as blocks of stacked-section columns (C1) and render it as
the ASCII-styled DOM grid (C2) with hover highlight and a select emit. Layout
mirrors the physical board (Client Satisfaction above Product Architecture;
Macroplan above Defect Visualisation, both left of Feature Kanban) and boxes
use true ISO 216 proportions (1:√2, each step up scaled by √2). Both views
render from the one definition; tests pin section presence, click, hover,
layout order, and a snapshot.

app/board/definition.ts

@@ -0,0 +1,65 @@
+// The canonical board (C1) — the single source both apps render from (F1).
+// Section `id`s are STABLE: defects reference them, so renaming a label is safe
+// but changing an id orphans existing defects. Add/rename here, then redeploy.
+//
+// Each block lays its sections out as COLUMNS of vertically-stacked sections,
+// mirroring the physical board (e.g. Macroplan above Defect Visualisation, both
+// to the left of Feature Kanban).
+
+export type PaperSize = 'A2' | 'A3' | 'A4'
+
+export interface Section {
+  id: string
+  label: string
+  size: PaperSize
+}
+
+export interface Block {
+  id: string
+  title: string
+  /** Left-to-right columns; each column is top-to-bottom sections. */
+  columns: Section[][]
+}
+
+export const board: Block[] = [
+  {
+    id: 'value-for-customer',
+    title: 'Value for Customer',
+    columns: [
+      [
+        { id: 'client-satisfaction', label: 'Client Satisfaction', size: 'A4' },
+        { id: 'product-architecture', label: 'Product Architecture', size: 'A4' },
+      ],
+    ],
+  },
+  {
+    id: 'right-first-time-jit',
+    title: 'Right First Time & Just in Time',
+    columns: [
+      [
+        { id: 'macroplan', label: 'Macroplan', size: 'A4' },
+        { id: 'defect-visualisation', label: 'Defect Visualisation', size: 'A4' },
+      ],
+      [{ id: 'feature-kanban', label: 'Feature Kanban', size: 'A2' }],
+    ],
+  },
+  {
+    id: 'tech-enabled-network',
+    title: 'Tech-Enabled Network of Teams',
+    columns: [[{ id: 'tech-working-condition', label: 'Tech Working Condition', size: 'A3' }]],
+  },
+  {
+    id: 'learning-organisation',
+    title: 'Building a Learning Organisation',
+    columns: [
+      [{ id: 'problem-solving', label: 'Problem Solving', size: 'A3' }],
+      [{ id: 'weak-point-management', label: 'Weak Point Management', size: 'A3' }],
+    ],
+  },
+]
+
+/** Flat list of every section, for lookups and validation. */
+export const sections: Section[] = board.flatMap((block) => block.columns.flat())
+
+/** Set of valid section ids — used server-side to validate filed defects. */
+export const sectionIds: ReadonlySet<string> = new Set(sections.map((s) => s.id))