feat(GRO-106): portal Communication tab — real backend

- Added GET /portal/conversation and GET /portal/conversation/messages endpoints
- Created Communication.api.ts with typed fetchers and React hooks
- Rewired Communication.tsx to use real API, removed mock data
- Added composer-disabled bar with "Reply from your phone" tooltip
- Added conversation route tests to portal.test.ts

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/api/src/lib/buffer.ts

@@ -0,0 +1,66 @@
+import { eq } from "@groombook/db";
+import { bufferTimeRules, services, type Db } from "@groombook/db";
+
+export async function resolveBufferMinutes({
+  serviceId,
+  sizeCategory,
+  coatType,
+  db,
+}: {
+  serviceId: string;
+  sizeCategory: string | null;
+  coatType: string | null;
+  db: Db;
+}): Promise<number> {
+  // Query all rules for this service in one DB call
+  const allRules = await db
+    .select()
+    .from(bufferTimeRules)
+    .where(eq(bufferTimeRules.serviceId, serviceId));
+
+  // Priority 1: exact match (serviceId + sizeCategory + coatType all match)
+  const exact = allRules.find(
+    (r) =>
+      r.sizeCategory === sizeCategory &&
+      r.coatType === coatType
+  );
+  if (exact) return exact.bufferMinutes;
+
+  // Priority 2: service + size, null coatType
+  const serviceSize = allRules.find(
+    (r) =>
+      r.sizeCategory === sizeCategory &&
+      r.coatType === null
+  );
+  if (serviceSize) return serviceSize.bufferMinutes;
+
+  // Priority 3: service + coat, null sizeCategory
+  const serviceCoat = allRules.find(
+    (r) =>
+      r.sizeCategory === null &&
+      r.coatType === coatType
+  );
+  if (serviceCoat) return serviceCoat.bufferMinutes;
+
+  // Priority 4: service only (null sizeCategory, null coatType)
+  const serviceOnly = allRules.find(
+    (r) =>
+      r.sizeCategory === null &&
+      r.coatType === null
+  );
+  if (serviceOnly) return serviceOnly.bufferMinutes;
+
+  // Priority 5: fallback to service.defaultBufferMinutes
+  const [service] = await db
+    .select({ defaultBufferMinutes: services.defaultBufferMinutes })
+    .from(services)
+    .where(eq(services.id, serviceId))
+    .limit(1);
+
+  if (service?.defaultBufferMinutes != null) {
+    return service.defaultBufferMinutes;
+  }
+
+  // Priority 6: final fallback to 0
+  return 0;
+}