feat(integration): DPD history tab — coverage, generation and backfill

A fourth tab on /officer/integration reading the loan book as a training
set. The verdict banner is the point of the screen: DPD history is the
model's label, and three thousand generated snapshots look identical on
a chart to three thousand real ones, so the split is stated in words at
the top rather than left to be inferred from a percentage.

Four tiles, and "unknown provenance" is one of them — rows written
before stamping existed are shown as their own bucket rather than
counted as real. Generation and purge sit beside a backfill-from-core
control, with the honest note that a backfill from a simulated adapter
produces simulated rows and only a bank's own core counts toward the
real total.

The demo fixture deliberately reports a book that is NOT trainable. A
fixture claiming a healthy training set would defeat the entire purpose
of the panel.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lib/api.ts

@@ -552,6 +552,61 @@ export interface ConnectorSyncResponse {
   preview?: ManualEntryPreview
 }
 
+/**
+ * The loan book read as a training set.
+ *
+ * <p>`verdict` is a sentence, not a number, because "is this trainable" is the
+ * only question that matters here and it must not be left to whoever is reading
+ * the percentages to work out.
+ */
+export interface LoanHistoryCoverage {
+  totalRecords: number
+  /** Rows this system generated. Never counts toward a real-data claim. */
+  syntheticRecords: number
+  realRecords: number
+  /** Rows written before provenance was stamped. Never counted as real. */
+  unknownProvenance: number
+  enterprisesTotal: number
+  enterprisesWithAnyLoan: number
+  enterprisesWithHistory: number
+  distinctAsOfDates: number
+  earliest: string | null
+  latest: string | null
+  historyCoveragePct: number
+  trainable: boolean
+  verdict: string
+}
+
+export interface LoanHistoryGenerateResult {
+  enterprises: number
+  loans: number
+  snapshotsWritten: number
+  monthsRequested: number
+  from: string | null
+  to: string | null
+  note: string
+}
+
+/** One month of one loan, as an extract reported it. */
+export interface LoanSnapshot {
+  id: number
+  accountRef: string
+  enterpriseId: string
+  product: string | null
+  sanctionedAmount: number | null
+  outstandingAmount: number | null
+  instalmentAmount: number | null
+  nextDueDate: string | null
+  lastPaidDate: string | null
+  dpd: number | null
+  bucket: string | null
+  closed: boolean
+  asOfDate: string
+  observedAt: string | null
+  /** SEEDED | SEEDED_HISTORY | UPLOAD | a connector profile code. */
+  source: string | null
+}
+
 /** The template a mapping targets, and the columns that may never be mapped in. */
 export interface CanonicalColumns {
   columns: string[]