feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/repositories/help_center.py

@@ -0,0 +1,129 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+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 datetime import datetime
+from typing import List, Optional
+from uuid import UUID
+
+from sqlalchemy.orm import Session
+
+from app.models.help_center import HelpCenterQuery, HelpCenterSettings
+
+# Both DNS records verified — the queryable form of the derived
+# HelpCenterSettings.domain_verified property.
+_DOMAIN_VERIFIED = (
+    HelpCenterSettings.txt_record_verified.is_(True)
+    & HelpCenterSettings.cname_record_verified.is_(True)
+)
+
+
+class HelpCenterRepository:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def get_by_org(self, organization_id: UUID) -> Optional[HelpCenterSettings]:
+        return (
+            self.db.query(HelpCenterSettings)
+            .filter(HelpCenterSettings.organization_id == organization_id)
+            .first()
+        )
+
+    def get_by_slug(self, slug: str) -> Optional[HelpCenterSettings]:
+        return (
+            self.db.query(HelpCenterSettings)
+            .filter(HelpCenterSettings.slug == slug.lower())
+            .first()
+        )
+
+    def get_by_verified_domain(self, domain: str) -> Optional[HelpCenterSettings]:
+        """Resolve a custom domain — only verified domains ever match, so an
+        unverified claim on someone else's hostname can't hijack serving."""
+        return (
+            self.db.query(HelpCenterSettings)
+            .filter(
+                HelpCenterSettings.custom_domain == domain.lower(),
+                _DOMAIN_VERIFIED,
+            )
+            .first()
+        )
+
+    def list_verified_domains(self) -> List[str]:
+        """All verified custom domains, for the host-dispatch cache."""
+        rows = (
+            self.db.query(HelpCenterSettings.custom_domain)
+            .filter(
+                HelpCenterSettings.custom_domain.isnot(None),
+                _DOMAIN_VERIFIED,
+            )
+            .all()
+        )
+        return [row[0] for row in rows]
+
+    def list_enabled_slugs(self) -> List[str]:
+        """Slugs of enabled help centers — their `{slug}.{base_domain}` origins
+        are added to the CORS allowlist for the embedded widget."""
+        rows = (
+            self.db.query(HelpCenterSettings.slug)
+            .filter(
+                HelpCenterSettings.enabled.is_(True),
+                HelpCenterSettings.slug.isnot(None),
+            )
+            .all()
+        )
+        return [row[0] for row in rows]
+
+    def slug_exists(self, slug: str) -> bool:
+        return self.db.query(
+            self.db.query(HelpCenterSettings)
+            .filter(HelpCenterSettings.slug == slug.lower())
+            .exists()
+        ).scalar()
+
+    def create(self, settings: HelpCenterSettings) -> HelpCenterSettings:
+        self.db.add(settings)
+        self.db.commit()
+        self.db.refresh(settings)
+        return settings
+
+    def update(self, settings: HelpCenterSettings) -> HelpCenterSettings:
+        self.db.commit()
+        self.db.refresh(settings)
+        return settings
+
+
+class HelpCenterQueryRepository:
+    def __init__(self, db: Session):
+        self.db = db
+
+    def log(self, organization_id: UUID, query: str, answered: bool) -> HelpCenterQuery:
+        row = HelpCenterQuery(organization_id=organization_id, query=query, answered=answered)
+        self.db.add(row)
+        self.db.commit()
+        return row
+
+    def count_for_period(self, organization_id: UUID, start: datetime, end: datetime) -> int:
+        """Answered asks in a billing period — feeds the hosted-model metering.
+        Half-open [start, end) so a boundary instant is never billed twice."""
+        return (
+            self.db.query(HelpCenterQuery)
+            .filter(
+                HelpCenterQuery.organization_id == organization_id,
+                HelpCenterQuery.answered.is_(True),
+                HelpCenterQuery.created_at >= start,
+                HelpCenterQuery.created_at < end,
+            )
+            .count()
+        )