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/composables/useOrchestration.svelte.ts

@@ -0,0 +1,151 @@
+import type { ChatMessage } from '$lib/types';
+import type { SubagentResult } from '$lib/proto/llm_multiverse/v1/common_pb';
+import type { SessionConfig } from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+import { processRequest, OrchestratorError, friendlyMessage } from '$lib/services/orchestrator';
+import { OrchestrationState } from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+import { sessionStore } from '$lib/stores/sessions.svelte';
+import { memoryStore } from '$lib/stores/memory.svelte';
+import { auditStore } from '$lib/stores/audit.svelte';
+import { toastStore } from '$lib/stores/toast.svelte';
+
+export function createOrchestration() {
+	let isStreaming = $state(false);
+	let error: string | null = $state(null);
+	let lastFailedContent: string | null = $state(null);
+	let orchestrationState: OrchestrationState = $state(OrchestrationState.UNSPECIFIED);
+	let intermediateResult: string = $state('');
+	let finalResult: SubagentResult | null = $state(null);
+
+	async function send(
+		sessionId: string,
+		content: string,
+		config: SessionConfig,
+		messages: ChatMessage[]
+	): Promise<ChatMessage[]> {
+		error = null;
+		lastFailedContent = null;
+		orchestrationState = OrchestrationState.UNSPECIFIED;
+		intermediateResult = '';
+		finalResult = null;
+
+		let lastAuditState = OrchestrationState.UNSPECIFIED;
+
+		const userMessage: ChatMessage = {
+			id: crypto.randomUUID(),
+			role: 'user',
+			content,
+			// eslint-disable-next-line svelte/prefer-svelte-reactivity -- plain data, not reactive state
+			timestamp: new Date()
+		};
+		messages.push(userMessage);
+
+		const assistantMessage: ChatMessage = {
+			id: crypto.randomUUID(),
+			role: 'assistant',
+			content: '',
+			// eslint-disable-next-line svelte/prefer-svelte-reactivity -- plain data, not reactive state
+			timestamp: new Date()
+		};
+		messages.push(assistantMessage);
+
+		sessionStore.updateMessages(sessionId, messages);
+		isStreaming = true;
+
+		try {
+			for await (const response of processRequest(sessionId, content, config)) {
+				orchestrationState = response.state;
+
+				if (response.state !== lastAuditState) {
+					const stateLabel = OrchestrationState[response.state] ?? String(response.state);
+					auditStore.addEvent(sessionId, {
+						eventType: 'state_change',
+						details: response.message || `State changed to ${stateLabel}`,
+						state: stateLabel
+					});
+					lastAuditState = response.state;
+				}
+
+				if (response.intermediateResult) {
+					intermediateResult = response.intermediateResult;
+				}
+				if (response.finalResult) {
+					finalResult = response.finalResult;
+					if (response.finalResult.newMemoryCandidates.length > 0) {
+						memoryStore.addCandidates(
+							sessionId,
+							response.finalResult.newMemoryCandidates.map((mc) => ({
+								content: mc.content,
+								source: mc.source,
+								confidence: mc.confidence
+							}))
+						);
+					}
+				}
+				const idx = messages.length - 1;
+				messages[idx] = {
+					...messages[idx],
+					content: response.message
+				};
+			}
+		} catch (err) {
+			const friendlyMsg =
+				err instanceof OrchestratorError
+					? friendlyMessage(err.code)
+					: 'An unexpected error occurred';
+			error = friendlyMsg;
+			lastFailedContent = content;
+			toastStore.addToast({ message: friendlyMsg, type: 'error' });
+			auditStore.addEvent(sessionId, {
+				eventType: 'error',
+				details: friendlyMsg
+			});
+			const idx = messages.length - 1;
+			messages[idx] = {
+				...messages[idx],
+				content: `\u26A0 ${friendlyMsg}`
+			};
+		} finally {
+			isStreaming = false;
+			sessionStore.updateMessages(sessionId, messages);
+		}
+
+		return messages;
+	}
+
+	function retry(
+		sessionId: string,
+		config: SessionConfig,
+		messages: ChatMessage[]
+	): { messages: ChatMessage[]; sending: boolean } {
+		if (!lastFailedContent) return { messages, sending: false };
+		const content = lastFailedContent;
+		// Remove the failed user+assistant pair before retrying
+		if (
+			messages.length >= 2 &&
+			messages[messages.length - 2].role === 'user' &&
+			messages[messages.length - 1].role === 'assistant' &&
+			messages[messages.length - 1].content.startsWith('\u26A0')
+		) {
+			messages = messages.slice(0, -2);
+		}
+		send(sessionId, content, config, messages);
+		return { messages, sending: true };
+	}
+
+	function reset() {
+		error = null;
+		finalResult = null;
+	}
+
+	return {
+		get isStreaming() { return isStreaming; },
+		get error() { return error; },
+		get lastFailedContent() { return lastFailedContent; },
+		get orchestrationState() { return orchestrationState; },
+		get intermediateResult() { return intermediateResult; },
+		get finalResult() { return finalResult; },
+		send,
+		retry,
+		reset
+	};
+}