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/specs/chat-ui/spec.md

@@ -25,7 +25,7 @@ The chat page SHALL display messages in a vertically scrolling list, with each m
 
 ### Requirement: Message input
 
-The chat page SHALL provide a text input area at the bottom of the page where the user can type and submit messages.
+The chat page SHALL provide a text input area at the bottom of the page where the user can type and submit messages. The input area SHALL also include a file upload button for triggering email extraction.
 
 #### Scenario: Submit via button
 
@@ -45,7 +45,12 @@ The chat page SHALL provide a text input area at the bottom of the page where th
 #### Scenario: Input disabled during streaming
 
 - **WHEN** the assistant is currently streaming a response
-- **THEN** the input field and send button are disabled until streaming completes
+- **THEN** the input field, send button, and upload button are disabled until streaming completes
+
+#### Scenario: Upload button opens file picker
+
+- **WHEN** the user clicks the upload button in the input area
+- **THEN** a file picker dialog opens filtered to .html files
 
 ### Requirement: Thinking indicator
 
@@ -100,9 +105,24 @@ The message list SHALL automatically scroll to the newest message when a new mes
 
 ### Requirement: Chat page is default route
 
-The chat page SHALL be the default route (`/`) of the application.
+The chat page SHALL be routed at `/sales-assistant` (or `/` with redirect). The page content SHALL be wrapped in a MudTabs container with the conversation UI in the first tab panel.
 
-#### Scenario: App opens to chat
+#### Scenario: App opens to chat via redirect
 
-- **WHEN** the user navigates to the root URL
+- **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
+
+#### Scenario: Page loads with chat tab active
+
+- **WHEN** the user navigates to the chat page
+- **THEN** the Chat tab is active showing the message list and input area
+
+#### Scenario: Chat functionality unchanged
+
+- **WHEN** the user sends a message from the Chat tab
+- **THEN** the assistant response streams in exactly as before, with the same SSE contract and rendering behavior