Add configurable plugin system and move hardcoded IP to config

Introduces a plugin registry so the display mode is selectable per
device via the NixOS module config (defaults to "calendar"). Moves
the hardcoded render URL base into config.base_url. Adds tests
exercising the plugin system with a synthetic ICS feed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/plugins.test.ts

@@ -0,0 +1,127 @@
+import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import type { Server } from 'bun';
+import { createPlugin } from './plugins';
+
+// --- Synthetic ICS ---
+
+const pad = (n: number) => n.toString().padStart(2, '0');
+const icsDate = (d: Date) =>
+  `${d.getFullYear()}${pad(d.getMonth() + 1)}${pad(d.getDate())}T${pad(d.getHours())}${pad(d.getMinutes())}00`;
+
+const now = new Date();
+const currentStart = new Date(now.getTime() - 30 * 60_000);
+const currentEnd = new Date(now.getTime() + 30 * 60_000);
+const nextStart = new Date(now.getTime() + 60 * 60_000);
+const nextEnd = new Date(now.getTime() + 120 * 60_000);
+const laterStart = new Date(now.getTime() + 180 * 60_000);
+const laterEnd = new Date(now.getTime() + 240 * 60_000);
+
+const ics = `BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+DTSTART:${icsDate(currentStart)}
+DTEND:${icsDate(currentEnd)}
+SUMMARY:Current Meeting
+UID:test-current@test
+END:VEVENT
+BEGIN:VEVENT
+DTSTART:${icsDate(nextStart)}
+DTEND:${icsDate(nextEnd)}
+SUMMARY:Next Meeting
+UID:test-next@test
+END:VEVENT
+BEGIN:VEVENT
+DTSTART:${icsDate(laterStart)}
+DTEND:${icsDate(laterEnd)}
+SUMMARY:Later Meeting
+UID:test-later@test
+END:VEVENT
+END:VCALENDAR`;
+
+const fakeModel = {
+  width: 800,
+  height: 480,
+  css: { classes: { device: 'device', size: 'size', density: 'density' } },
+} as any;
+
+// --- ICS server ---
+
+let icsServer: Server;
+let icsUrl: string;
+
+beforeAll(() => {
+  icsServer = Bun.serve({
+    port: 0,
+    hostname: '127.0.0.1',
+    routes: {
+      '/cal.ics': () =>
+        new Response(ics, {
+          headers: { 'Content-Type': 'text/calendar' },
+        }),
+    },
+  });
+  icsUrl = `http://127.0.0.1:${icsServer.port}/cal.ics`;
+});
+
+afterAll(() => {
+  icsServer.stop();
+});
+
+// --- Tests ---
+
+describe('plugin registry', () => {
+  test('unknown plugin throws', () => {
+    expect(() => createPlugin('nonexistent', {})).toThrow(
+      'Unknown plugin: nonexistent'
+    );
+  });
+
+  test('calendar plugin creates an ICSRenderable', () => {
+    const plugin = createPlugin('calendar', { urls: [] });
+    expect(plugin.hash).toBe('');
+    expect(plugin.nextEvent).toBeUndefined();
+  });
+});
+
+describe('calendar plugin rendering', () => {
+  test('renders events from ICS feed', async () => {
+    const plugin = createPlugin('calendar', { urls: [icsUrl] });
+    const html = await plugin.render('full', fakeModel);
+
+    expect(html).toContain('Current Meeting');
+    expect(html).toContain('Next Meeting');
+    expect(html).toContain('Later Meeting');
+  });
+
+  test('shows BEZET when there is a current event', async () => {
+    const plugin = createPlugin('calendar', { urls: [icsUrl] });
+    const html = await plugin.render('full', fakeModel);
+
+    expect(html).toContain('BEZET');
+  });
+
+  test('computes hash after render', async () => {
+    const plugin = createPlugin('calendar', { urls: [icsUrl] });
+    await plugin.render('full', fakeModel);
+
+    expect(plugin.hash).toBeTruthy();
+  });
+
+  test('sets nextEvent to upcoming event start', async () => {
+    const plugin = createPlugin('calendar', { urls: [icsUrl] });
+    await plugin.render('full', fakeModel);
+
+    expect(plugin.nextEvent).toBeInstanceOf(Date);
+    const diff = Math.abs(plugin.nextEvent!.getTime() - nextStart.getTime());
+    expect(diff).toBeLessThan(120_000);
+  });
+
+  test('renders VRIJ with no events', async () => {
+    const plugin = createPlugin('calendar', { urls: [] });
+    const html = await plugin.render('full', fakeModel);
+
+    expect(html).toContain('VRIJ');
+    expect(html).not.toContain('BEZET');
+  });
+});