feat: Add conversational AI assistant panel for project codebase Q&A

Implement a slide-in chat panel that allows users to ask questions about
their codebase using Claude Opus 4.5 with read-only access to project files.

Backend changes:
- Add SQLAlchemy models for conversation persistence (assistant_database.py)
- Create AssistantChatSession with read-only Claude SDK client
- Add WebSocket endpoint for real-time chat streaming
- Include read-only MCP tools: feature_get_stats, feature_get_next, etc.

Frontend changes:
- Add floating action button (bottom-right) to toggle panel
- Create slide-in panel component (400px width)
- Implement WebSocket hook with reconnection logic
- Add keyboard shortcut 'A' to toggle assistant

Key features:
- Read-only access: Only Read, Glob, Grep, WebFetch, WebSearch tools
- Persistent history: Conversations saved to SQLite per project
- Real-time streaming: Text chunks streamed as Claude generates response
- Tool visibility: Shows when assistant is using tools to explore code

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/lib/api.ts

@@ -14,6 +14,8 @@ import type {
   SetupStatus,
   DirectoryListResponse,
   PathValidationResponse,
+  AssistantConversation,
+  AssistantConversationDetail,
 } from './types'
 
 const API_BASE = '/api'
@@ -228,3 +230,40 @@ export async function validatePath(path: string): Promise<PathValidationResponse
     body: JSON.stringify({ path }),
   })
 }
+
+// ============================================================================
+// Assistant Chat API
+// ============================================================================
+
+export async function listAssistantConversations(
+  projectName: string
+): Promise<AssistantConversation[]> {
+  return fetchJSON(`/assistant/conversations/${encodeURIComponent(projectName)}`)
+}
+
+export async function getAssistantConversation(
+  projectName: string,
+  conversationId: number
+): Promise<AssistantConversationDetail> {
+  return fetchJSON(
+    `/assistant/conversations/${encodeURIComponent(projectName)}/${conversationId}`
+  )
+}
+
+export async function createAssistantConversation(
+  projectName: string
+): Promise<AssistantConversation> {
+  return fetchJSON(`/assistant/conversations/${encodeURIComponent(projectName)}`, {
+    method: 'POST',
+  })
+}
+
+export async function deleteAssistantConversation(
+  projectName: string,
+  conversationId: number
+): Promise<void> {
+  await fetchJSON(
+    `/assistant/conversations/${encodeURIComponent(projectName)}/${conversationId}`,
+    { method: 'DELETE' }
+  )
+}

ui/src/lib/types.ts

@@ -229,3 +229,69 @@ export interface ChatMessage {
   questions?: SpecQuestion[]
   isStreaming?: boolean
 }
+
+// ============================================================================
+// Assistant Chat Types
+// ============================================================================
+
+export interface AssistantConversation {
+  id: number
+  project_name: string
+  title: string | null
+  created_at: string | null
+  updated_at: string | null
+  message_count: number
+}
+
+export interface AssistantMessage {
+  id: number
+  role: 'user' | 'assistant' | 'system'
+  content: string
+  timestamp: string | null
+}
+
+export interface AssistantConversationDetail {
+  id: number
+  project_name: string
+  title: string | null
+  created_at: string | null
+  updated_at: string | null
+  messages: AssistantMessage[]
+}
+
+export interface AssistantChatTextMessage {
+  type: 'text'
+  content: string
+}
+
+export interface AssistantChatToolCallMessage {
+  type: 'tool_call'
+  tool: string
+  input: Record<string, unknown>
+}
+
+export interface AssistantChatResponseDoneMessage {
+  type: 'response_done'
+}
+
+export interface AssistantChatErrorMessage {
+  type: 'error'
+  content: string
+}
+
+export interface AssistantChatConversationCreatedMessage {
+  type: 'conversation_created'
+  conversation_id: number
+}
+
+export interface AssistantChatPongMessage {
+  type: 'pong'
+}
+
+export type AssistantChatServerMessage =
+  | AssistantChatTextMessage
+  | AssistantChatToolCallMessage
+  | AssistantChatResponseDoneMessage
+  | AssistantChatErrorMessage
+  | AssistantChatConversationCreatedMessage
+  | AssistantChatPongMessage