feat: add extraction schema, sidebar nav, few-shot prompting, and prompt settings

Overhaul extraction pipeline with new TradeItem model, conversation flow,
and dedicated extraction endpoint. Add sidebar navigation with NavMenu
component and landing page. Introduce few-shot prompting service and
tests. Add prompt settings and email upload specs. Update OpenSpec
tooling with improved export-spec and extract-feature commands. Archive
completed changes and export full specs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/archive/2026-04-06-add-sidebar-navigation/proposal.md

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+## Why
+
+The app currently has no navigation — just a single page at `/`. Adding a sidebar drawer with navigation enables the app to grow to multiple pages while providing standard MudBlazor layout structure (AppBar + Drawer + MainContent).
+
+## What Changes
+
+- Add a MudDrawer to MainLayout with a NavMenu component containing a "Sales Assistant" link
+- Add a hamburger toggle button in the AppBar to open/close the drawer
+- Move the existing chat page from `/` to `/sales-assistant`
+- Add a landing page or redirect at `/` so the app has a default route
+
+## Capabilities
+
+### New Capabilities
+- `sidebar-navigation`: Collapsible sidebar drawer with navigation menu, hamburger toggle, and route structure
+
+### Modified Capabilities
+- `chat-ui`: Route changes from `/` to `/sales-assistant`
+
+## Impact
+
+- **MainLayout.razor**: Add MudDrawer, hamburger icon, drawer toggle state
+- **New NavMenu component**: Shared/NavMenu.razor with MudNavGroup/MudNavLink items
+- **Chat.razor**: Route changes from `@page "/"` to `@page "/sales-assistant"`
+- **Chat.razor.css**: Height calc may need adjustment if AppBar Dense changes
+- No new packages — MudDrawer/MudNavMenu are part of MudBlazor