Goal

Create the /settings page in the web UI with navigation skeleton and the Agent Settings section.

Background

Currently all config is via env vars or CLI. A new user who can't find the env vars cannot use the product. This is an onboarding blocker.

Scope

• Create /settings route in Next.js App Router with a sidebar-tabbed layout (Agent / API Keys / PROOF9 / Workspace tabs — stubs for tabs beyond Agent are fine)
• Agent settings form (first tab, fully functional):
  • Default model per agent type: Claude Code, Codex, OpenCode, ReAct — dropdown per type using the models returned by GET /api/v2/agents/config (or equivalent)
  • Max turns per task (integer input, default 20)
  • Max cost per task in USD (decimal input)
• Wire up GET /api/v2/settings and PUT /api/v2/settings (or equivalent backend endpoint — add it if missing)
• Save / discard with toast feedback

Out of scope

• API key tab, PROOF9 tab, workspace tab (separate issues)
• No multi-user permission checks

Acceptance criteria

• /settings renders with sidebar nav
• Agent settings load on mount from the API
• Edits persist after page reload
• npm test and npm run build pass