feat(pitch-deck): full pitch versioning with git-style history (#4)

Full pitch versioning: 12 data tables versioned as JSONB snapshots,
git-style parent chain (draft→commit→fork), per-investor assignment,
side-by-side diff engine, version-aware /api/data + /api/financial-model.

Bug fixes: FM editor [object Object] for JSONB arrays, admin scroll.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pitch-deck/lib/version-diff.ts

@@ -0,0 +1,102 @@
+export interface FieldDiff {
+  key: string
+  before: unknown
+  after: unknown
+}
+
+export interface RowDiff {
+  status: 'added' | 'removed' | 'changed' | 'unchanged'
+  id?: string | number
+  fields: FieldDiff[]
+  before?: Record<string, unknown>
+  after?: Record<string, unknown>
+}
+
+export interface TableDiff {
+  tableName: string
+  rows: RowDiff[]
+  hasChanges: boolean
+}
+
+/**
+ * Diff two arrays of row objects. Matches rows by `id` field if present,
+ * otherwise by array position.
+ */
+export function diffTable(
+  tableName: string,
+  before: unknown[],
+  after: unknown[],
+): TableDiff {
+  const beforeArr = (before || []) as Record<string, unknown>[]
+  const afterArr = (after || []) as Record<string, unknown>[]
+
+  const rows: RowDiff[] = []
+
+  // Build lookup by id if available
+  const hasIds = beforeArr.length > 0 && 'id' in (beforeArr[0] || {})
+
+  if (hasIds) {
+    const beforeMap = new Map(beforeArr.map(r => [String(r.id), r]))
+    const afterMap = new Map(afterArr.map(r => [String(r.id), r]))
+    const allIds = new Set([...beforeMap.keys(), ...afterMap.keys()])
+
+    for (const id of allIds) {
+      const b = beforeMap.get(id)
+      const a = afterMap.get(id)
+
+      if (!b && a) {
+        rows.push({ status: 'added', id: a.id as string, fields: [], after: a })
+      } else if (b && !a) {
+        rows.push({ status: 'removed', id: b.id as string, fields: [], before: b })
+      } else if (b && a) {
+        const fields = diffFields(b, a)
+        rows.push({
+          status: fields.length > 0 ? 'changed' : 'unchanged',
+          id: b.id as string,
+          fields,
+          before: b,
+          after: a,
+        })
+      }
+    }
+  } else {
+    // Positional comparison
+    const maxLen = Math.max(beforeArr.length, afterArr.length)
+    for (let i = 0; i < maxLen; i++) {
+      const b = beforeArr[i]
+      const a = afterArr[i]
+      if (!b && a) {
+        rows.push({ status: 'added', fields: [], after: a })
+      } else if (b && !a) {
+        rows.push({ status: 'removed', fields: [], before: b })
+      } else if (b && a) {
+        const fields = diffFields(b, a)
+        rows.push({
+          status: fields.length > 0 ? 'changed' : 'unchanged',
+          fields,
+          before: b,
+          after: a,
+        })
+      }
+    }
+  }
+
+  return {
+    tableName,
+    rows,
+    hasChanges: rows.some(r => r.status !== 'unchanged'),
+  }
+}
+
+function diffFields(before: Record<string, unknown>, after: Record<string, unknown>): FieldDiff[] {
+  const diffs: FieldDiff[] = []
+  const allKeys = new Set([...Object.keys(before), ...Object.keys(after)])
+  for (const key of allKeys) {
+    const bVal = JSON.stringify(before[key] ?? null)
+    const aVal = JSON.stringify(after[key] ?? null)
+    if (bVal !== aVal) {
+      diffs.push({ key, before: before[key], after: after[key] })
+    }
+  }
+  return diffs
+}