refactor: code review improvements — fix bugs, extract shared utilities, add README

- Fix reactivity bug: use SvelteMap instead of Map in sessions store
- Fix theme listener memory leak: guard against double-init, return cleanup function
- Fix transport singleton ignoring different endpoints
- Fix form/button type mismatch in MessageInput
- Add safer retry validation in chat page
- Extract shared utilities: date formatting, session config check, result source config
- Extract shared components: Backdrop, PageHeader
- Extract orchestration composable from chat page (310→85 lines of script)
- Consolidate AuditTimeline switch functions into config record
- Move sample data to dedicated module
- Add dark mode support for LineageTree SVG colors
- Memoize leaf count computation in LineageTree
- Update README with usage guide and project structure

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/services/orchestrator.ts

@@ -79,15 +79,18 @@ function getTransport(endpoint?: string) {
 /**
  * Reset the transport (useful for reconfiguring the endpoint).
  */
-export function resetTransport(): void {
+export function resetTransport(newEndpoint?: string): void {
 	transport = null;
+	if (newEndpoint !== undefined) {
+		transport = createGrpcWebTransport({ baseUrl: newEndpoint });
+	}
 }
 
 /**
  * Create a configured orchestrator client.
  */
-function getClient(endpoint?: string) {
-	return createClient(OrchestratorService, getTransport(endpoint));
+function getClient() {
+	return createClient(OrchestratorService, getTransport());
 }
 
 /**
@@ -147,8 +150,7 @@ function toOrchestratorError(err: unknown): OrchestratorError {
 export async function* processRequest(
 	sessionId: string,
 	userMessage: string,
-	sessionConfig?: SessionConfig,
-	endpoint?: string
+	sessionConfig?: SessionConfig
 ): AsyncGenerator<ProcessRequestResponse> {
 	const request = create(ProcessRequestRequestSchema, {
 		sessionId,
@@ -166,7 +168,7 @@ export async function* processRequest(
 		}
 
 		try {
-			const client = getClient(endpoint);
+			const client = getClient();
 			for await (const response of client.processRequest(request)) {
 				connectionStore.reportSuccess();
 				yield response;