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/utils/sessionConfig.ts

@@ -0,0 +1,13 @@
+import { OverrideLevel } from '$lib/proto/llm_multiverse/v1/common_pb';
+import type { SessionConfig } from '$lib/proto/llm_multiverse/v1/orchestrator_pb';
+
+/**
+ * Returns true if the session config differs from defaults.
+ */
+export function isNonDefaultConfig(config: SessionConfig): boolean {
+	return (
+		config.overrideLevel !== OverrideLevel.NONE ||
+		config.disabledTools.length > 0 ||
+		config.grantedPermissions.length > 0
+	);
+}