feat(customer): 网站客户身份签发与长期负责人绑定

可信客户身份由站点后端签发，长期负责人与本次接待人分开保存。

backend/app/services/contact_capture.py

@@ -0,0 +1,88 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+from typing import Optional, Dict, Any
+from app.repositories.customer import CustomerRepository
+
+# Where a handoff email goes when the customer row can't take it — another
+# customer in the org already owns that address (the (email, organization_id)
+# unique constraint), or it is a channel identity key. meta_data renders as a
+# label/value list in the inbox customer panel, so an agent still sees the
+# address and can follow up. Dropping it is how a visitor asks to be contacted
+# and then never is.
+CONTACT_EMAIL_META_KEY = "contact_email_provided"
+
+
+def retain_unstored_email(customer_repo, customer_id, submitted_email: str, update_result: dict) -> bool:
+    """Keep a submitted handoff email that ``update_contact`` could not apply.
+
+    Returns True when it was retained on meta_data. No-op when the address did
+    land on the customer, when it is already their stored address, or when
+    nothing was submitted — so a normal capture writes no metadata.
+    """
+    if not submitted_email or update_result.get('email_updated'):
+        return False
+    stored = (update_result.get('email') or '').lower()
+    if submitted_email.lower() == stored:
+        return False
+    return customer_repo.update_meta_data(
+        customer_id, {CONTACT_EMAIL_META_KEY: submitted_email}
+    ) is not None
+
+
+def build_handoff_contact_form(
+    customer,
+    collect_email: bool,
+    collect_name: bool,
+) -> Optional[Dict[str, Any]]:
+    """Return ``form_data`` (``form_type='contact'``) for the handoff contact prompt, or
+    ``None`` when there is nothing to collect (toggles off, or the customer already has the
+    info). The widget renders this with its existing inline form UI.
+    """
+    if customer is None:
+        return None
+
+    needs_email = bool(collect_email) and CustomerRepository.is_placeholder_email(getattr(customer, 'email', None))
+    full_name = (getattr(customer, 'full_name', None) or '').strip()
+    needs_name = bool(collect_name) and not full_name
+
+    if not needs_email and not needs_name:
+        return None
+
+    fields = []
+    if needs_email:
+        fields.append({
+            'name': 'email',
+            'type': 'email',
+            'label': 'Email',
+            'placeholder': 'you@example.com',
+            'required': True,
+        })
+    if needs_name:
+        fields.append({
+            'name': 'name',
+            'type': 'text',
+            'label': 'Name',
+            'placeholder': 'Your name',
+            'required': False,
+        })
+
+    return {
+        'form_type': 'contact',
+        'title': 'Before we connect you to a teammate',
+        'description': 'Share your details so we can follow up.',
+        'fields': fields,
+    }