feat: redesign day picker with expandable calendar, status markers & Playwright E2E testing

- Replace modal calendar with inline expandable calendar widget integrated into the day picker.
- Add status indicator dots (attended/absent/pending) to month calendar grid matching day picker.
- Disable and gray out weekend days in calendar when weekend schedule is turned off.
- Redesign extend bar with integrated handle that aligns with the palette.
- Remove start-to-end timing on Today screen's class time rail, showing only start time.
- Implement Playwright E2E and visual testing suite with multi-screen capture scripts.
- Add cascade DELETE endpoints for subjects and versioned recurring timetable entries.

scripts/capture-friday.mjs

@@ -0,0 +1,23 @@
+import { chromium } from 'playwright';
+
+async function captureFriday() {
+  const browser = await chromium.launch({ headless: true });
+  const context = await browser.newContext({
+    viewport: { width: 390, height: 844 },
+    deviceScaleFactor: 2,
+    isMobile: true,
+  });
+  const page = await context.newPage();
+  await page.goto('http://127.0.0.1:3000/');
+  await page.waitForTimeout(2000);
+  // Click on the Friday date card (date number 4)
+  const fridayCell = page.locator('text=fri').locator('..');
+  if (await fridayCell.isVisible()) {
+    await fridayCell.click();
+    await page.waitForTimeout(1000);
+  }
+  await page.screenshot({ path: './screenshots/01-today-friday.png' });
+  await browser.close();
+}
+
+captureFriday().catch(console.error);