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/prompt-settings-ui/spec.md

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+## Purpose
+
+Define the UI controls for configuring system prompt and model parameters — tabbed layout, prompt editor, and settings controls.
+
+## Requirements
+
+### Requirement: System prompt editor tab
+
+The chat page SHALL include a "System Prompt" tab with a multi-line text area where the user can enter a system prompt. The system prompt value SHALL persist across tab switches within the same session.
+
+#### Scenario: User enters a system prompt
+
+- **WHEN** the user navigates to the System Prompt tab and types text
+- **THEN** the text is stored in the component state and included in the next chat request
+
+#### Scenario: System prompt survives tab switch
+
+- **WHEN** the user enters a system prompt, switches to the Chat tab, then switches back
+- **THEN** the system prompt text is unchanged
+
+### Requirement: Model settings tab
+
+The chat page SHALL include a "Model Settings" tab with controls for Temperature, TopP, and MaxTokens. Each control SHALL display its current value and allow adjustment within valid ranges.
+
+#### Scenario: Temperature control
+
+- **WHEN** the user adjusts the Temperature control
+- **THEN** the value is constrained to 0.0–2.0 and included in the next chat request's settings
+
+#### Scenario: TopP control
+
+- **WHEN** the user adjusts the TopP control
+- **THEN** the value is constrained to 0.0–1.0 and included in the next chat request's settings
+
+#### Scenario: MaxTokens control
+
+- **WHEN** the user sets the MaxTokens value
+- **THEN** the value is constrained to 1–4096 and included in the next chat request's settings
+
+#### Scenario: Default values
+
+- **WHEN** the user has not changed any model settings
+- **THEN** the controls show default values (Temperature: 1.0, TopP: 1.0, MaxTokens: empty/unset) and no overrides are sent to the API
+
+### Requirement: Tabbed page layout
+
+The chat page SHALL use MudTabs with three tab panels: "Chat" (the existing conversation UI), "System Prompt" (the prompt editor), and "Model Settings" (the parameter controls).
+
+#### Scenario: Chat tab is default
+
+- **WHEN** the page loads
+- **THEN** the Chat tab is active and the conversation UI is displayed
+
+#### Scenario: Tab switching
+
+- **WHEN** the user clicks a different tab
+- **THEN** the corresponding panel is displayed and the previous panel is hidden but retains its state