Three-panel admin workspace: left reference panel (submission details,
vendor data), center editor (refined scope, inline line item table with
reorder/add/remove/pricing), right similar proposals panel (KB results
with pull-to-editor). Admin dashboard with stats cards and proposal
queue table. Approval flow with confirmation dialog, mark-as-sent,
and create-revision actions. Role-based sidebar navigation.
Backend endpoint POST /api/auth/callback exchanges the OAuth
authorization code with Cognito's token endpoint, auto-provisions
the user in the DB, and returns the access token to the frontend.
