feat(apps): a sales expert can work inside their customer's account (D29)

Reported missing by the owner: in the reference an expert could open any
of their referred customers and use the app AS them — browse, see
balance and debt, place orders — «یکجورایی انگار با اکانت اون ها لاگین
کرده». D21 had deliberately left it out as a session-hijack primitive.
The owner asked for the capability back with the implementation left to
judgement, so the scope is the reference's and the mechanism is not.

Scope: everything, as the reference had it. Its axios interceptor
swapped the bearer token, so every request went as the customer,
document upload included. No route is closed in act-as mode.

Mechanism: the reference minted and handed over the customer's own
permanent api_token. Here the expert keeps their own token and sends
X-Act-As-Customer, resolved in one place — CustomerJwtStrategy
.validateExpert. That single point is why all 17 customer routes work
unchanged: validate() already returns a principal whose `id` is a
Customer id and every customer route reads it. It also fixes four real
defects of the original:

  - ownership is re-checked on EVERY request, with referredByAgentId in
    the same where clause as the id, so another expert's customer and a
    non-existent id both answer 403, and a customer moved to another
    expert loses access at once rather than at token expiry;
  - nothing durable is handed out — the reference's token sat in
    localStorage with no expiry and kept working after the expert left;
  - adminUserId survives, so an order placed this way is attributable;
    in the reference the request was literally the customer's;
  - 403 rather than 401, so the app clears the act-as state instead of
    logging a perfectly valid session out.

Performance: one findFirst on the primary key, only when the header is
present, and it replaces the trading-account lookup rather than adding
to it.

Three things the reference never needed, because it swapped the whole
session. queryCache's `me:` keys, favouritesStore and wageQuoteStore all
dropped their data on a TOKEN change, which act-as does not cause — so
an expert would have seen their own profile, orders, balance, ledger and
favourites inside the customer's account. The wage-quote one is the
money case: making charge is per customer, so the figure on screen would
not have been the one the order was priced at. And uploadDocument builds
its own headers, so an expert's upload would have been filed against
their own account, silently.

Added with no reference equivalent: a permanent «در حال مشاهده به‌عنوان
…» bar. There, impersonation was invisible once the token had been
swapped, and placing an order on the wrong customer's gold debt was one
tap away. It is also the exit — the reference's only way out was a
logout that ended the expert's own session too. The cart is cleared in
both directions.

CustomerJwtStrategy had no test coverage at all and is now where this
feature's whole authorisation boundary lives: act-as-customer.spec.ts
covers 11 cases, including the header being ignored on a customer token,
the no-header path asserting the extra query does not run, and a revoked
session short-circuiting before the header is read.

api: 308/308 tests, 28 suites; both apps vue-tsc clean.

اپ: کارشناس فروش می‌تواند وارد حساب مشتریان خود شود، وضعیتشان را ببیند و از طرفشان سفارش ثبت کند.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/user-app/src/components/expert/ActingAsBar.vue

@@ -0,0 +1,112 @@
+<!--
+  «در حال مشاهده به‌عنوان …» — shown while a sales expert is working inside one
+  of their customers' accounts.
+
+  NOT in the reference, and added on purpose. There, impersonation was invisible
+  once the token had been swapped (myDataStore.ts:163): the only way an expert
+  could tell whose account they were in was to notice the data looked wrong.
+  Placing an order on the wrong customer's account — their gold debt, their
+  ledger — was a single tap away with nothing to catch it.
+
+  It is also the exit. The reference's only way out was the logout button, which
+  dropped the expert's own session too (Dashboard.vue:781-789).
+-->
+<template>
+  <div v-if="session.actingAs" class="aab" role="status">
+    <span class="aab__dot" aria-hidden="true" />
+    <span class="aab__text">
+      در حال مشاهده به‌عنوان <strong>{{ session.actingAs.name || 'مشتری' }}</strong>
+    </span>
+    <button type="button" class="aab__exit" :disabled="leaving" @click="leave">
+      {{ leaving ? '…' : 'خروج' }}
+    </button>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref } from 'vue'
+import { useRouter } from 'vue-router'
+import { useSessionStore } from '../../stores/session'
+import { useCartStore } from '../../stores/cartStore'
+import { toast } from '../../composables/useToast'
+
+const session = useSessionStore()
+const cart = useCartStore()
+const router = useRouter()
+const leaving = ref(false)
+
+/**
+ * Back to the expert's own account. The cart is cleared in this direction too:
+ * a basket built inside the customer's account must not follow the expert out
+ * and land on their own order.
+ */
+async function leave() {
+  leaving.value = true
+  try {
+    cart.clear()
+    session.setActingAs(null)
+    await router.push({ name: 'home' })
+    toast.info('به حساب خودتان بازگشتید')
+  } finally {
+    leaving.value = false
+  }
+}
+</script>
+
+<style scoped lang="less">
+.aab {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  z-index: 2000;
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 7px 16px;
+  /* Deliberately not a brand colour: this is a warning strip, and it has to be
+     noticeable at a glance to do its job. */
+  background: #8d6a46;
+  color: #fff;
+  font-size: 12px;
+  font-weight: 600;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.18);
+}
+
+.aab__dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  background: #ffd9a0;
+  flex: 0 0 auto;
+}
+
+.aab__text {
+  flex: 1 1 auto;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+
+  strong {
+    font-weight: 800;
+  }
+}
+
+.aab__exit {
+  flex: 0 0 auto;
+  border: 1px solid rgba(255, 255, 255, 0.55);
+  background: transparent;
+  color: #fff;
+  border-radius: 8px;
+  padding: 3px 12px;
+  font-family: inherit;
+  font-size: 12px;
+  font-weight: 700;
+  cursor: pointer;
+
+  &:disabled {
+    opacity: 0.6;
+    cursor: default;
+  }
+}
+</style>