Test: TS-07 returning user with existing display_name skips set-name

Inverse coverage for the auth path: TS-01..TS-06 all wipe the customer
row (drop_customer=true) so every OTP path lands on the new-user
set-name branch. TS-07 instead seeds an existing identified customer
(phone + display_name + is_anonymous=false) and verifies the OTP
sign-in returns the existing row unchanged via
resolveCustomerForIdentity branch 1, so /auth/set-name is never shown.

Adds:
* /internal/_test/seed-customer endpoint — upserts a customer with
  phone + display_name + is_anonymous=false.
* client_app/.maestro/scripts/seed_customer.js helper.
* client_app/.maestro/flows/ts-07_returning_existing_name_skips_setname.yaml.
* TS-07 scenario doc + coverage-map row in
  requirement/phase4-customer-flow.md.

The flow asserts the "halo, <name>" greeting on the returning-user home
variant (identified users always land on _SHomeReturningView regardless
of chat history) plus an explicit notVisible on "Siapa namamu" as a
belt-and-braces check.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/routes/internal/_test.routes.js

@@ -306,6 +306,29 @@ export const internalTestRoutes = async (fastify) => {
     return { ok: true, payment_id: row.id, ...row }
   })
 
+  // Upsert a customer row with phone + display_name (is_anonymous=false).
+  // Used by Maestro TS-07 to set up the "returning user already has a name"
+  // precondition: a real returning OTP sign-in must skip the set-name screen
+  // because resolveCustomerForIdentity returns the existing row unchanged.
+  //
+  // Body: { phone, display_name }
+  fastify.post('/seed-customer', async (request, reply) => {
+    const phone = request.body?.phone
+    const display_name = request.body?.display_name
+    if (!phone || !display_name) {
+      return reply.code(400).send({ error: 'phone and display_name required in body' })
+    }
+    const [row] = await sql`
+      INSERT INTO customers (phone, display_name, is_anonymous)
+      VALUES (${phone}, ${display_name}, false)
+      ON CONFLICT (phone) DO UPDATE
+        SET display_name = EXCLUDED.display_name,
+            is_anonymous = false
+      RETURNING id, phone, display_name, is_anonymous
+    `
+    return { ok: true, ...row }
+  })
+
   // Mark EVERY mitra row online. Used by Maestro flows as a setup step to
   // ensure a clean known-good state regardless of what previous tests did
   // (e.g. force-mitra-offline leaving the dev DB with no online mitras).