feat(drill): ProviderDrawer with Overview tab + DrillDrawerHeader shell

src/lib/api.ts

@@ -16,7 +16,8 @@
  *   - `parse835(...)` mirrors the 837 shape for `/api/parse-835`.
  *   - `health()` GETs `/api/health` and returns `{ status, version }`.
  *   - `listBatches / getBatch / listClaims / listRemittances / listProviders
- *     / listActivity` are plain JSON GETs against the persistence surface.
+ *     / getProvider / listActivity` are plain JSON GETs against the
+ *     persistence surface.
  *   - `listUnmatched / matchRemit / unmatchClaim` hit the reconciliation
  *     surface. POSTs throw `ApiError` so callers can branch on `.status`.
  */
@@ -36,6 +37,7 @@ import type {
   Payer,
   Payer835,
   Payee835,
+  Provider,
   ReassociationTrace,
   UnmatchedClaim,
   UnmatchedResponse,
@@ -586,6 +588,33 @@ async function listProviders<T = unknown>(
   return (await res.json()) as PaginatedResponse<T>;
 }
 
+/**
+ * Fetch one configured provider by NPI, used by the provider drill-down
+ * drawer (SP21 Task 2.2 / 1.6).
+ *
+ * Drives ``GET /api/config/providers/{npi}``. Note the ``/api/config/``
+ * prefix — this is the config-side route namespace, distinct from the
+ * persistence-side ``/api/providers`` used by ``listProviders``. The
+ * response is the full ``Provider`` shape (including the optional
+ * ``recent_claims`` and ``recent_activity`` arrays populated by Task
+ * 1.6 when the backend can serve them).
+ *
+ * Throws ``ApiError`` on non-2xx — including 404, which the drawer may
+ * want to branch on for a "provider no longer configured" state.
+ */
+async function getProvider(npi: string): Promise<Provider> {
+  if (!isConfigured) throw notConfiguredError();
+  const res = await fetch(
+    joinUrl(`/api/config/providers/${encodeURIComponent(npi)}`),
+    { headers: { Accept: "application/json" } }
+  );
+  if (!res.ok) {
+    const detail = await readErrorBody(res);
+    throw new ApiError(res.status, detail || res.statusText);
+  }
+  return (await res.json()) as Provider;
+}
+
 /**
  * Aggregate stats for one payer, used by the peek modal on Dashboard /
  * Claims tables (SP21 universal drill-down). Drives
@@ -773,6 +802,7 @@ export const api = {
   listRemittances,
   getRemittance,
   listProviders,
+  getProvider,
   getPayerSummary,
   listActivity,
   listUnmatched,