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/alembic/versions/040_add_user_profile_fields.py

@@ -0,0 +1,30 @@
+"""Add user profile fields (phone, job_title, timezone, avatar_url, email_verified_at)
+
+Revision ID: 040
+Revises: fb1481317ff6
+Create Date: 2026-03-03
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers
+revision = "040"
+down_revision = "e2d81e82ea5e"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("users", sa.Column("phone", sa.String(50), nullable=True))
+    op.add_column("users", sa.Column("job_title", sa.String(255), nullable=True))
+    op.add_column("users", sa.Column("timezone", sa.String(100), nullable=False, server_default="UTC"))
+    op.add_column("users", sa.Column("avatar_url", sa.String(500), nullable=True))
+    op.add_column("users", sa.Column("email_verified_at", sa.DateTime(timezone=True), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("users", "email_verified_at")
+    op.drop_column("users", "avatar_url")
+    op.drop_column("users", "timezone")
+    op.drop_column("users", "job_title")
+    op.drop_column("users", "phone")