feat: add audit/activity log view with timeline and event filtering (#17)

Add a dedicated /audit route displaying a chronological timeline of
orchestration events (state transitions, tool invocations, errors,
messages) grouped by session. Includes session selector, event type
filtering, URL deep-linking via ?session=id, and audit event capture
during chat streaming.

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

src/routes/chat/+page.svelte

@@ -19,6 +19,7 @@
 	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';
 
 	let messages: ChatMessage[] = $state([]);
 	let isStreaming = $state(false);
@@ -32,6 +33,7 @@
 	let showConfig = $state(false);
 	const lineageHref = resolveRoute('/lineage');
 	const memoryHref = resolveRoute('/memory');
+	const auditHref = resolveRoute('/audit');
 
 	const isNonDefaultConfig = $derived(
 		sessionConfig.overrideLevel !== OverrideLevel.NONE ||
@@ -80,6 +82,7 @@
 		finalResult = null;
 
 		const sessionId = sessionStore.activeSessionId!;
+		let lastAuditState = OrchestrationState.UNSPECIFIED;
 
 		const userMessage: ChatMessage = {
 			id: crypto.randomUUID(),
@@ -103,6 +106,18 @@
 		try {
 			for await (const response of processRequest(sessionId, content, sessionConfig)) {
 				orchestrationState = response.state;
+
+				// Capture state changes to the audit log
+				if (response.state !== lastAuditState) {
+					const stateLabel = OrchestrationState[response.state] ?? String(response.state);
+					auditStore.addEvent(sessionId, {
+						eventType: 'state_change',
+						details: response.message || `State changed to ${stateLabel}`,
+						state: stateLabel
+					});
+					lastAuditState = response.state;
+				}
+
 				if (response.intermediateResult) {
 					intermediateResult = response.intermediateResult;
 				}
@@ -131,6 +146,10 @@
 					? `Error (${err.code}): ${err.message}`
 					: 'An unexpected error occurred';
 			error = msg;
+			auditStore.addEvent(sessionId, {
+				eventType: 'error',
+				details: msg
+			});
 			const idx = messages.length - 1;
 			messages[idx] = {
 				...messages[idx],
@@ -163,6 +182,12 @@
 			>
 				Memory
 			</a>
+			<a
+				href={auditHref}
+				class="rounded-lg px-2.5 py-1.5 text-sm text-gray-600 hover:bg-gray-100 hover:text-gray-900"
+			>
+				Audit
+			</a>
 			<!-- eslint-enable svelte/no-navigation-without-resolve -->
 			<button
 				type="button"