fix(calendar): skip malformed ical events

[keilogic]

Summary

Closes #1484.

This makes calendar event loading tolerant of malformed iCalendar data. If one stored event fails while parsing or generating display occurrences, the service now reports that event through the existing errorLog path and keeps loading the remaining valid events.

The first commit adds the regression test by itself so it can be cherry-picked separately. The second commit contains the implementation.

Tests

• npx ng test --watch=false --browsers=FirefoxHeadless --include=src/app/calendar-app/calendar.service.spec.ts - 10 SUCCESS
• npx tsc -p tsconfig.json --noEmit
• git diff --check
• Manual production build steps on Windows PowerShell:
  • node src/build/pre-build.js
  • npx ng build runbox7 --configuration production --base-href /app/
  • node src/build/post-build.js
• npx ng test --watch=false --browsers=FirefoxHeadless - 246 SUCCESS, 2 skipped
• npm run lint - exits 0 with the repository's existing warning baseline
• npm run policy - exits 0; it still prints existing historical commit-message warnings outside this branch

Note: the build pre-step regenerated src/app/changelog/changes.ts, but I did not include that generated file so this PR stays scoped to the calendar fix.

AI Disclosure

I used OpenAI Codex while working on this PR. Codex assisted with editing src/app/calendar-app/calendar.service.ts and src/app/calendar-app/calendar.service.spec.ts; I reviewed the diff and ran the validation commands above locally.

[castaway]

Could you put the "broken" ical value not all on one long line (newlines are fine), and document what exactly is "broken" in the test data?

[castaway]

hi @keilogic could you respond to the requested changes?