feat: a calendar to subscribe to, and the backlog's corners

- Each person can subscribe their dates in Google Calendar, Outlook or
  Apple Calendar: GET /api/calendar/{token}.ics (no session) brings
  their unfinished tickets with a due date (assigned or followed), the
  planned and running sprints and the planned releases of their
  projects, as all-day events linking to the web. The token is made,
  renewed or dropped under /me/calendar (and in GraphQL); in the web,
  from «Calendario» in «Mi trabajo».
- The backlog panel keeps the selected rows' background inside its
  rounded corners.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/application/src/lib/calendar/ics.spec.ts

@@ -0,0 +1,62 @@
+import { buildIcs } from './ics';
+
+const NOW = new Date('2026-10-14T09:30:00.000Z');
+
+describe('buildIcs', () => {
+  it('writes all-day events with an exclusive end', () => {
+    const ics = buildIcs(
+      'TaskStream',
+      [
+        {
+          uid: 'issue-1@taskstream',
+          start: '2026-10-20',
+          summary: 'WEB-1 · Login',
+        },
+        {
+          uid: 'sprint-1@taskstream',
+          start: '2026-10-05',
+          end: '2026-10-19',
+          summary: 'Sprint 4',
+        },
+      ],
+      NOW,
+    );
+    expect(ics.startsWith('BEGIN:VCALENDAR\r\nVERSION:2.0\r\n')).toBe(true);
+    expect(ics.endsWith('END:VCALENDAR\r\n')).toBe(true);
+    expect(ics).toContain('DTSTAMP:20261014T093000Z');
+    expect(ics).toContain(
+      'DTSTART;VALUE=DATE:20261020\r\nDTEND;VALUE=DATE:20261021',
+    );
+    expect(ics).toContain(
+      'DTSTART;VALUE=DATE:20261005\r\nDTEND;VALUE=DATE:20261020',
+    );
+    expect(ics.split('BEGIN:VEVENT')).toHaveLength(3);
+  });
+
+  it('escapes text and skips what has no date', () => {
+    const ics = buildIcs(
+      'Ana; López, QA',
+      [
+        { uid: 'a', start: '2026-10-20', summary: 'Pago; roto, en\nSafari' },
+        { uid: 'b', start: '', summary: 'sin fecha' },
+      ],
+      NOW,
+    );
+    expect(ics).toContain('X-WR-CALNAME:Ana\\; López\\, QA');
+    expect(ics).toContain('SUMMARY:Pago\\; roto\\, en\\nSafari');
+    expect(ics).not.toContain('sin fecha');
+  });
+
+  it('folds long lines at 75 octets without splitting a character', () => {
+    const summary = 'Revisión de la exportación á'.repeat(5);
+    const ics = buildIcs(
+      'x',
+      [{ uid: 'u', start: '2026-10-20', summary }],
+      NOW,
+    );
+    for (const line of ics.split('\r\n'))
+      expect(Buffer.byteLength(line, 'utf8')).toBeLessThanOrEqual(75);
+    // Unfolding gives the text back.
+    expect(ics.replace(/\r\n /g, '')).toContain(`SUMMARY:${summary}`);
+  });
+});