[feature] Make context explorer available to all users (read-only)

[ClaireGz]

Problem

The context explorer is currently admin-only. Business users have no way to browse what data is available to nao - they can't see which tables, metrics, or rules exist. This forces them to guess what they can ask about, or ping the data team to find out.

Expected behavior

• All users (including regular/business users) can access a read-only view of the context explorer - it's available at the bottom of left side bar, above settings
• The view should be user-friendly and non-technical - e.g. browsable list of available tables, descriptions, key metrics (see issue [feature] Redesign file explorer page #933)
• No editing capabilities for regular users - just browsing

Client_ID: EA