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/specs/sidebar-navigation/spec.md

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+## ADDED Requirements
+
+### Requirement: Collapsible sidebar drawer
+
+The application SHALL have a MudDrawer in MainLayout that contains a navigation menu. The drawer SHALL be toggleable via a hamburger icon button in the AppBar.
+
+#### Scenario: Drawer visible on load
+
+- **WHEN** the application loads
+- **THEN** the sidebar drawer is displayed in its default open state with navigation links visible
+
+#### Scenario: Drawer toggles on hamburger click
+
+- **WHEN** the user clicks the hamburger icon in the AppBar
+- **THEN** the drawer toggles between open and collapsed states
+
+### Requirement: Navigation menu with Sales Assistant link
+
+The sidebar drawer SHALL contain a MudNavMenu with a "Sales Assistant" navigation link that routes to `/sales-assistant`.
+
+#### Scenario: Sales Assistant link present
+
+- **WHEN** the drawer is open
+- **THEN** a "Sales Assistant" link with a SmartToy icon is visible in the navigation menu
+
+#### Scenario: Clicking Sales Assistant navigates to chat
+
+- **WHEN** the user clicks the "Sales Assistant" link
+- **THEN** the browser navigates to `/sales-assistant` and the chat page renders in MudMainContent
+
+### Requirement: NavMenu is a separate component
+
+The navigation menu SHALL be implemented as a separate `NavMenu.razor` component in the Layout folder, referenced from MainLayout.
+
+#### Scenario: NavMenu renders inside drawer
+
+- **WHEN** MainLayout renders
+- **THEN** the NavMenu component renders inside the MudDrawer with its navigation links