feat: add account management, email verification, AI fixes, and user guides

- Profile settings, account transfer, delete/leave account flows
- Email verification with JWT tokens and Resend integration
- AI assistant/copilot fixes: markdown rendering, shared RAG helpers,
  token tracking, input refocus, model_validate usage
- User guides hub + detail pages with 13 topic guides
- Sidebar and top bar navigation for guides

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/email_verification_token.py

@@ -0,0 +1,42 @@
+import uuid
+from datetime import datetime, timezone
+from typing import Optional
+from sqlalchemy import String, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID
+from app.core.database import Base
+
+
+class EmailVerificationToken(Base):
+    __tablename__ = "email_verification_tokens"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        primary_key=True,
+        default=uuid.uuid4
+    )
+    token_hash: Mapped[str] = mapped_column(String(64), unique=True, nullable=False, index=True)
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id"),
+        nullable=False,
+        index=True
+    )
+    expires_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
+    used_at: Mapped[Optional[datetime]] = mapped_column(DateTime(timezone=True), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc)
+    )
+
+    @property
+    def is_used(self) -> bool:
+        return self.used_at is not None
+
+    @property
+    def is_expired(self) -> bool:
+        return datetime.now(timezone.utc) > self.expires_at
+
+    @property
+    def is_valid(self) -> bool:
+        return not self.is_used and not self.is_expired

backend/app/models/user.py

@@ -68,6 +68,15 @@ class User(Base):
     )
     last_login: Mapped[Optional[datetime]] = mapped_column(DateTime(timezone=True), nullable=True)
 
+    # Profile fields
+    phone: Mapped[Optional[str]] = mapped_column(String(50), nullable=True)
+    job_title: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
+    timezone: Mapped[str] = mapped_column(String(100), nullable=False, default="UTC", server_default="UTC")
+    avatar_url: Mapped[Optional[str]] = mapped_column(String(500), nullable=True)
+    email_verified_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+
     # AI billing cycle anchor (for quota reset calculation)
     ai_billing_cycle_anchor_at: Mapped[Optional[datetime]] = mapped_column(
         DateTime(timezone=True), nullable=True