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/tasks.md

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+## 1. MainLayout: Add Drawer and Hamburger Toggle
+
+- [x] 1.1 Add a `_drawerOpen` bool field (default `true`) and a `ToggleDrawer` method to MainLayout.razor
+- [x] 1.2 Add a `MudIconButton` with `Icons.Material.Filled.Menu` as the first element in the MudAppBar, wired to `ToggleDrawer`
+- [x] 1.3 Add a `MudDrawer` with `Open="@_drawerOpen"`, `ClipMode="DrawerClipMode.Always"`, `Elevation="2"` inside the MudLayout, before MudMainContent
+- [x] 1.4 Reference `<NavMenu />` inside the MudDrawer
+
+## 2. NavMenu Component
+
+- [x] 2.1 Create `Layout/NavMenu.razor` with a `MudNavMenu` containing a single `MudNavLink` — text "Sales Assistant", icon `Icons.Material.Filled.SmartToy`, href `/sales-assistant`
+- [x] 2.2 Add inline tutorial comments explaining MudNavMenu, MudNavLink, and how href-based navigation works in Blazor
+
+## 3. Chat Page Route Change
+
+- [x] 3.1 Change `Chat.razor` route from `@page "/"` to `@page "/sales-assistant"`
+- [x] 3.2 Update the page title from "Chat Agent" to "Sales Assistant"
+
+## 4. Root Redirect
+
+- [x] 4.1 Create a `Pages/Index.razor` component at `@page "/"` that redirects to `/sales-assistant` on initialization using `NavigationManager.NavigateTo` (Home.razor already exists as health check page at /health)
+
+## 5. Chat Container Height Adjustment
+
+- [x] 5.1 Verify `Chat.razor.css` height calc still works with the drawer layout — Dense AppBar is 48px, drawer does not affect vertical space. Adjust if needed.
+
+## 6. Verification
+
+- [x] 6.1 Build the client project (`dotnet build`) and confirm no compilation errors
+- [x] 6.2 Run existing tests (`dotnet test`) and confirm they pass