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/tests/test_email_verification.py

@@ -0,0 +1,57 @@
+"""Tests for email verification endpoints."""
+
+import pytest
+from httpx import AsyncClient
+
+
+@pytest.mark.asyncio
+class TestEmailVerification:
+    """Test email verification send + verify flow."""
+
+    async def test_send_verification(self, client: AsyncClient, auth_headers: dict):
+        """Send verification email returns 200."""
+        response = await client.post(
+            "/api/v1/auth/email/send-verification",
+            headers=auth_headers,
+        )
+        assert response.status_code == 200
+        assert "sent" in response.json()["message"].lower()
+
+    async def test_send_verification_already_verified(
+        self, client: AsyncClient, auth_headers: dict, test_db
+    ):
+        """Returns 400 if email is already verified."""
+        from sqlalchemy import select, update
+        from datetime import datetime, timezone
+        from app.models.user import User
+
+        # Manually mark email as verified
+        await test_db.execute(
+            update(User).where(User.email == "test@example.com").values(
+                email_verified_at=datetime.now(timezone.utc)
+            )
+        )
+        await test_db.commit()
+
+        response = await client.post(
+            "/api/v1/auth/email/send-verification",
+            headers=auth_headers,
+        )
+        assert response.status_code == 400
+        assert "already verified" in response.json()["detail"].lower()
+
+    async def test_verify_invalid_token(self, client: AsyncClient):
+        """Invalid token returns 400."""
+        response = await client.post(
+            "/api/v1/auth/email/verify",
+            json={"token": "invalid-token"},
+        )
+        assert response.status_code == 400
+
+    async def test_verify_missing_token(self, client: AsyncClient):
+        """Missing token returns 400."""
+        response = await client.post(
+            "/api/v1/auth/email/verify",
+            json={},
+        )
+        assert response.status_code == 400