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/041_add_email_verification_tokens.py

@@ -0,0 +1,30 @@
+"""Add email_verification_tokens table
+
+Revision ID: 041
+Revises: 040
+Create Date: 2026-03-03
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision = "041"
+down_revision = "040"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "email_verification_tokens",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("token_hash", sa.String(64), unique=True, nullable=False, index=True),
+        sa.Column("user_id", postgresql.UUID(as_uuid=True), sa.ForeignKey("users.id"), nullable=False, index=True),
+        sa.Column("expires_at", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("used_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("email_verification_tokens")