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/models/help_center.py

@@ -0,0 +1,134 @@
+"""
+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.
+"""
+
+import enum
+import uuid
+
+from sqlalchemy import Boolean, CheckConstraint, Column, DateTime, ForeignKey, JSON, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+DEFAULT_BRAND_COLOR = "#4338CA"
+DEFAULT_CTA_TEXT = "Contact us"
+
+
+class DomainStatus(str, enum.Enum):
+    UNVERIFIED = "unverified"
+    PENDING = "pending"
+    VERIFIED = "verified"
+
+
+class SSLStatus(str, enum.Enum):
+    NONE = "none"
+    PENDING = "pending"
+    ACTIVE = "active"
+    FAILED = "failed"
+
+
+class HelpCenterSettings(Base):
+    """Per-org public help center configuration (branding, agent mapping,
+    subdomain slug and optional custom domain). One row per organization,
+    created lazily the first time the org opens the FAQ admin page.
+    """
+    __tablename__ = "help_center_settings"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    organization_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("organizations.id", ondelete="CASCADE"),
+        nullable=False,
+        unique=True,
+    )
+    # Whether the public site is live at {slug}.{HELP_CENTER_BASE_DOMAIN}.
+    enabled = Column(Boolean, nullable=False, default=False)
+    slug = Column(String(63), unique=True, nullable=True, index=True)
+
+    # Branding
+    title = Column(String(120), nullable=True)
+    description = Column(String(300), nullable=True)
+    logo_url = Column(String, nullable=True)
+    favicon_url = Column(String, nullable=True)
+    brand_color = Column(String(9), nullable=False, default=DEFAULT_BRAND_COLOR)
+    # [{"label": str, "url": str}, ...]
+    header_links = Column(JSON, nullable=False, default=lambda: [])
+    cta_text = Column(String(40), nullable=True, default=DEFAULT_CTA_TEXT)
+    cta_url = Column(String, nullable=True)
+    # Whether the primary button (CTA) is shown in the public header.
+    cta_enabled = Column(Boolean, nullable=False, default=True)
+
+    # Draft FAQs are auto-generated when a new knowledge source finishes.
+    auto_generate = Column(Boolean, nullable=False, default=True)
+
+    # Which agent grounds "Ask AI" answers and whose chat widget is embedded on
+    # the public page. The two surfaces toggle independently:
+    #   - ai_search_enabled: the inline AI quick-summary answer in search.
+    #   - chat_widget_enabled: the embedded chat widget ("Start a chat").
+    agent_id = Column(UUID(as_uuid=True), ForeignKey("agents.id", ondelete="SET NULL"), nullable=True)
+    ai_search_enabled = Column(Boolean, nullable=False, default=True)
+    chat_widget_enabled = Column(Boolean, nullable=False, default=True)
+
+    # Custom domain. Verification state is the two per-record booleans; the
+    # aggregate status is derived (see domain_status) so the pieces can never
+    # disagree.
+    custom_domain = Column(String(255), unique=True, nullable=True, index=True)
+    domain_verification_token = Column(String(64), nullable=True)
+    txt_record_verified = Column(Boolean, nullable=False, default=False)
+    cname_record_verified = Column(Boolean, nullable=False, default=False)
+    # Plain string (values from SSLStatus) — an external fact set by the
+    # verification probe, stored like knowledge_queue's string statuses.
+    ssl_status = Column(String, nullable=False, default=SSLStatus.NONE)
+    domain_verified_at = Column(DateTime(timezone=True), nullable=True)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    organization = relationship("Organization")
+    agent = relationship("Agent")
+
+    __table_args__ = (
+        CheckConstraint("slug = lower(slug)", name="ck_help_center_slug_lowercase"),
+    )
+
+    @property
+    def domain_verified(self) -> bool:
+        return bool(self.custom_domain) and self.txt_record_verified and self.cname_record_verified
+
+    @property
+    def domain_status(self) -> DomainStatus:
+        if not self.custom_domain:
+            return DomainStatus.UNVERIFIED
+        return DomainStatus.VERIFIED if self.domain_verified else DomainStatus.PENDING
+
+
+class HelpCenterQuery(Base):
+    """Log of public "Ask AI" questions — used for per-period metering on
+    hosted models and (later) search analytics. No answer text is stored.
+    """
+    __tablename__ = "help_center_queries"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    organization_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("organizations.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    query = Column(Text, nullable=False)
+    answered = Column(Boolean, nullable=False, default=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), index=True)