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

scripts/capture-timeline.mjs

@@ -0,0 +1,24 @@
+import { chromium } from 'playwright';
+import path from 'node:path';
+
+const url = process.argv[2] || 'http://localhost:3003/timeline';
+
+const shots = [
+  { name: 'desktop', width: 1440, height: 900 },
+];
+
+const browser = await chromium.launch({ headless: true });
+
+for (const shot of shots) {
+  const page = await browser.newPage({ viewport: { width: shot.width, height: shot.height } });
+  await page.goto(url, { waitUntil: 'domcontentloaded' });
+  await page.waitForTimeout(2000);
+  await page.screenshot({
+    path: path.join('artifacts', `timeline-${shot.name}.png`),
+    fullPage: true,
+  });
+  await page.close();
+}
+
+await browser.close();
+console.log('Screenshot saved to artifacts/timeline-desktop.png');