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/chat-ui/spec.md

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+## MODIFIED Requirements
+
+### 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 input area SHALL also include a file upload button for triggering email extraction.
+
+#### Scenario: Submit via button
+
+- **WHEN** the user types text and clicks the send button
+- **THEN** the message is added to the conversation and the input is cleared
+
+#### Scenario: Submit via Enter key
+
+- **WHEN** the user types text and presses Enter
+- **THEN** the message is submitted (same as clicking send)
+
+#### Scenario: Empty input blocked
+
+- **WHEN** the user attempts to send an empty or whitespace-only message
+- **THEN** nothing is sent and no message is added
+
+#### Scenario: Input disabled during streaming
+
+- **WHEN** the assistant is currently streaming a response
+- **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

openspec/changes/archive/2026-04-06-email-upload-ux/specs/email-upload/spec.md

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+## ADDED Requirements
+
+### Requirement: Drag-and-drop email upload
+
+The chat message area SHALL accept files dragged from the desktop or file explorer. When a supported file is dropped, the client SHALL read the file content and send it to the extraction endpoint.
+
+#### Scenario: Drag HTML file onto chat
+
+- **WHEN** the user drags an .html file over the message area
+- **THEN** a visual drop indicator appears (e.g., highlighted border, overlay text "Drop email here")
+
+#### Scenario: Drop HTML file triggers extraction
+
+- **WHEN** the user drops an .html file onto the message area
+- **THEN** the client reads the HTML content, sends it to `POST /api/chat/extract`, and streams the extraction response in the chat
+
+#### Scenario: Unsupported file type rejected
+
+- **WHEN** the user drops a non-.html file (e.g., .pdf, .docx)
+- **THEN** the client shows a brief error message indicating only .html files are supported
+
+### Requirement: File picker upload button
+
+The chat input area SHALL include an upload button (e.g., attachment icon) that opens a file picker dialog for selecting .html email files.
+
+#### Scenario: Upload via file picker
+
+- **WHEN** the user clicks the upload button and selects an .html file
+- **THEN** the client reads the HTML content and sends it to the extraction endpoint, same as drag-and-drop
+
+### Requirement: Upload disabled during streaming
+
+The upload zone and file picker SHALL be disabled while a response is streaming.
+
+#### Scenario: Drop during streaming
+
+- **WHEN** the user attempts to drop a file while the assistant is streaming
+- **THEN** the drop is ignored and no extraction request is sent

openspec/changes/archive/2026-04-06-email-upload-ux/specs/extraction-conversation-flow/spec.md

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+## 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