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-email-upload-ux/specs/extraction-conversation-flow/spec.md

@@ -0,0 +1,47 @@
+## ADDED Requirements
+
+### Requirement: Extraction mode tracking
+
+The chat page SHALL track whether the current conversation is in extraction mode. Extraction mode is entered when an email is uploaded and exited when the user starts a new chat.
+
+#### Scenario: Enter extraction mode on upload
+
+- **WHEN** the user uploads an email file
+- **THEN** the conversation enters extraction mode and subsequent messages are routed to the extraction endpoint
+
+#### Scenario: Exit extraction mode on New Chat
+
+- **WHEN** the user clicks "New Chat" while in extraction mode
+- **THEN** the conversation exits extraction mode and returns to general chat routing
+
+### Requirement: Extraction mode visual indicator
+
+The chat page SHALL display a visual indicator when in extraction mode so the user knows their messages are part of an extraction conversation.
+
+#### Scenario: Indicator shown in extraction mode
+
+- **WHEN** the conversation is in extraction mode
+- **THEN** a visual indicator (e.g., chip, banner, or subtitle) is visible showing the extraction context
+
+#### Scenario: Indicator hidden in general mode
+
+- **WHEN** the conversation is in general chat mode
+- **THEN** no extraction indicator is shown
+
+### Requirement: Follow-up messages route to extraction endpoint
+
+In extraction mode, text messages typed by the user SHALL be sent to the extraction endpoint with the original email HTML and full conversation history, not to the general chat endpoint.
+
+#### Scenario: User replies to disambiguation question
+
+- **WHEN** the agent asks "Which legal entity?" and the user types "1"
+- **THEN** the client sends an ExtractionRequest with the original email HTML plus all messages (assistant question + user reply) to `POST /api/chat/extract`
+
+### Requirement: Email upload message in chat
+
+When an email is uploaded, the chat SHALL display a user message indicating the upload (e.g., showing the filename) before the extraction response streams in.
+
+#### Scenario: Upload message displayed
+
+- **WHEN** the user drops "trade_request.html"
+- **THEN** a user message appears in the chat like "[Uploaded: trade_request.html]" followed by the streaming extraction response