feat(GRO-106): STOP/HELP compliance + consent log

- Add detectKeyword() and handleConsentKeyword() in consent.ts
- Wire keyword detection into handleMessageReceived() in inbound.ts
- Add 24-unit test suite for consent.ts covering all keywords,
  case insensitivity, whitespace tolerance, idempotency, and
  help keyword state preservation

Fixes from QA review:
- Use getDb() instead of non-existent db export; import Db type
- Destructure clientId from findOrCreateConversation result
- Rename staffId → sentByStaffId in sendMessage call
- Remove messagingHelpReply query (column not yet in schema)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/services/messaging/consent.ts

@@ -0,0 +1,77 @@
+import { getDb, clients, messageConsentEvents, eq } from "@groombook/db";
+import type { Db } from "@groombook/db";
+
+export type KeywordKind = "opt_in" | "opt_out" | "help";
+
+const OPT_OUT_KEYWORDS = new Set(["STOP", "STOPALL", "UNSUBSCRIBE", "CANCEL", "END", "QUIT"]);
+const OPT_IN_KEYWORDS = new Set(["START", "UNSTOP", "YES", "SUBSCRIBE"]);
+const HELP_KEYWORDS = new Set(["HELP", "INFO"]);
+
+export function detectKeyword(body: string): { kind: KeywordKind } | null {
+  const normalized = body.trim().toUpperCase();
+  if (OPT_OUT_KEYWORDS.has(normalized)) return { kind: "opt_out" };
+  if (OPT_IN_KEYWORDS.has(normalized)) return { kind: "opt_in" };
+  if (HELP_KEYWORDS.has(normalized)) return { kind: "help" };
+  return null;
+}
+
+export async function handleConsentKeyword(opts: {
+  clientId: string;
+  businessId: string;
+  kind: KeywordKind;
+  db: Db;
+}): Promise<{ replyText: string }> {
+  const { clientId, businessId, kind, db: database } = opts;
+
+  await database.insert(messageConsentEvents).values({
+    clientId,
+    businessId,
+    kind,
+    source: "sms_keyword",
+  });
+
+  if (kind === "opt_out") {
+    const [existing] = await database
+      .select({ smsOptIn: clients.smsOptIn })
+      .from(clients)
+      .where(eq(clients.id, clientId))
+      .limit(1);
+
+    if (existing?.smsOptIn !== false) {
+      await database
+        .update(clients)
+        .set({ smsOptIn: false, smsOptOutDate: new Date() })
+        .where(eq(clients.id, clientId));
+    }
+
+    return {
+      replyText: "You have been unsubscribed and will no longer receive messages. Reply START to resubscribe.",
+    };
+  }
+
+  if (kind === "opt_in") {
+    const [existing] = await database
+      .select({ smsOptIn: clients.smsOptIn, smsConsentDate: clients.smsConsentDate })
+      .from(clients)
+      .where(eq(clients.id, clientId))
+      .limit(1);
+
+    if (existing?.smsOptIn !== true) {
+      await database
+        .update(clients)
+        .set({ smsOptIn: true, smsConsentDate: new Date(), smsOptOutDate: null })
+        .where(eq(clients.id, clientId));
+    }
+
+    return {
+      replyText:
+        "You have been resubscribed to messages. Reply STOP to unsubscribe. Msg & data rates may apply.",
+    };
+  }
+
+  // kind === "help"
+  const replyText =
+    "Reply STOP to unsubscribe or START to resubscribe. For help, contact your groomer directly.";
+
+  return { replyText };
+}