Update shared access docs
docs: document Shared Access (delegated users) feature New Shared-Access page covers the delegate invitation flow (existing user, owner-set password, email invite), the three-tab permission modal (Accounts / Sections / Shared data), the "Viewing:" context banner, password reset rules, removal, and the 2FA requirement. Cross-referenced from Home and Settings and Security. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>