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/chat-ui/spec.md

@@ -0,0 +1,15 @@
+## MODIFIED Requirements
+
+### Requirement: Chat page is default route
+
+The chat page SHALL be routed at `/sales-assistant`. The root URL (`/`) SHALL redirect to `/sales-assistant`.
+
+#### Scenario: App opens to chat via redirect
+
+- **WHEN** the user navigates to the root URL `/`
+- **THEN** the browser redirects to `/sales-assistant` and the chat page is displayed
+
+#### Scenario: Direct navigation to sales-assistant
+
+- **WHEN** the user navigates to `/sales-assistant`
+- **THEN** the chat page is displayed