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

tests/components/sessions/sessions-header-logic.test.ts

@@ -0,0 +1,68 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { getSwarmHealth } from '../../../src/components/sessions/sessions-header-logic';
+import type { AgentRecord, AgentLiveness } from '../../../src/lib/agent-registry';
+
+// Mock AgentRecord helper
+function mockAgent(id: string, liveness: AgentLiveness): { agent: AgentRecord, liveness: AgentLiveness } {
+  return {
+    agent: {
+      agent_id: id,
+      display_name: id,
+      role: 'agent',
+      status: 'idle',
+      created_at: new Date().toISOString(),
+      last_seen_at: new Date().toISOString(),
+      version: 1
+    },
+    liveness
+  };
+}
+
+test('getSwarmHealth returns green/active when all agents are active', () => {
+  const members = [
+    mockAgent('a1', 'active'),
+    mockAgent('a2', 'active')
+  ];
+  const livenessMap = { a1: 'active', a2: 'active' };
+  
+  const health = getSwarmHealth(members.map(m => m.agent), livenessMap);
+  assert.equal(health.status, 'active');
+  assert.equal(health.color, 'text-emerald-400');
+});
+
+test('getSwarmHealth returns yellow/warning when any agent is stale', () => {
+  const members = [
+    mockAgent('a1', 'active'),
+    mockAgent('a2', 'stale')
+  ];
+  const livenessMap = { a1: 'active', a2: 'stale' };
+  
+  const health = getSwarmHealth(members.map(m => m.agent), livenessMap);
+  assert.equal(health.status, 'warning');
+  assert.equal(health.color, 'text-amber-400');
+});
+
+test('getSwarmHealth returns red/critical when any agent is evicted/dead', () => {
+  const members = [
+    mockAgent('a1', 'active'),
+    mockAgent('a2', 'evicted')
+  ];
+  const livenessMap = { a1: 'active', a2: 'evicted' };
+  
+  const health = getSwarmHealth(members.map(m => m.agent), livenessMap);
+  assert.equal(health.status, 'critical');
+  assert.equal(health.color, 'text-rose-400');
+});
+
+test('getSwarmHealth returns gray/offline when all agents are idle', () => {
+  const members = [
+    mockAgent('a1', 'idle'),
+    mockAgent('a2', 'idle')
+  ];
+  const livenessMap = { a1: 'idle', a2: 'idle' };
+  
+  const health = getSwarmHealth(members.map(m => m.agent), livenessMap);
+  assert.equal(health.status, 'offline');
+  assert.equal(health.color, 'text-zinc-500');
+});