chore: add utility scripts and additional test coverage

STORY:
Development requires supporting scripts and comprehensive test coverage.
This commit adds utility scripts and extends test suites.

COLLABORATION:
- scripts/capture-sessions.mjs: Screenshot capture for sessions hub
- scripts/capture-timeline.mjs: Timeline view capture utility
- sessions-header-logic.ts: Session header business logic
- Additional test files for sessions, hooks, and snapshot diffing

src/components/sessions/sessions-header-logic.ts

@@ -0,0 +1,47 @@
+import type { AgentRecord, AgentLiveness } from '../../lib/agent-registry';
+
+export interface SwarmHealth {
+  status: 'active' | 'warning' | 'critical' | 'offline';
+  color: string;
+}
+
+export function getSwarmHealth(
+  members: AgentRecord[],
+  livenessMap: Record<string, AgentLiveness | string>
+): SwarmHealth {
+  if (members.length === 0) {
+    return { status: 'offline', color: 'text-zinc-500' };
+  }
+
+  let hasStale = false;
+  let hasEvicted = false;
+  let allIdle = true;
+
+  for (const member of members) {
+    const liveness = livenessMap[member.agent_id] as AgentLiveness || 'active';
+    
+    if (liveness !== 'idle') {
+      allIdle = false;
+    }
+
+    if (liveness === 'stale') {
+      hasStale = true;
+    } else if (liveness === 'evicted') {
+      hasEvicted = true;
+    }
+  }
+
+  if (allIdle) {
+    return { status: 'offline', color: 'text-zinc-500' };
+  }
+
+  if (hasEvicted) {
+    return { status: 'critical', color: 'text-rose-400' };
+  }
+
+  if (hasStale) {
+    return { status: 'warning', color: 'text-amber-400' };
+  }
+
+  return { status: 'active', color: 'text-emerald-400' };
+}