Hierarchical Administration Settings Navigation

[yuanzui-cf]

Objective

Use a dedicated full-height navigation hierarchy for Administration settings, consistent with other nested Console areas.

Acceptance Criteria

• Administration settings include Basic Settings, Website Announcements, Governance Policies, Infrastructure, and Runtime Settings.
• Entering Administration settings replaces the full sidebar with settings-specific navigation.
• The settings sidebar provides a return action to Administration.
• The Administration sidebar and its existing return-to-Console behavior remain unchanged.
• The content area no longer duplicates settings navigation with tabs.
• Existing settings, save behavior, and error states remain unchanged.
• Legacy settings URLs redirect to Basic Settings.
• Desktop and mobile routing and navigation have regression coverage.