feat(calendar): open event meeting links from the events card

[floydya]

Summary

Resolve a clickable meeting link for calendar events and make linked events open in the browser from the control center events card.

Motivation

Meeting URLs already arrive with every sync - Google and Outlook write them into LOCATION, but LOCATION was stored and never displayed, and the URL property was not parsed at all. Joining a meeting meant leaving the shell and finding the event in a browser.

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Build / packaging

Related Issue

None

Testing

• tests/event_link_test.cpp (new, registered in meson.build): 24 cases covering bare/embedded links, trailing punctuation and wrappers, LOCATION-over-URL precedence, scheme rejection (file:, data:, webcal:, mailto:), control characters, length cap, and token-boundary matching.
• tests/ical_parser_test.cpp: three VEVENT fixtures - LOCATION link wins over URL, URL fallback, and no link.
• Both test binaries built and run: pass.
• just format (clang-format v22).
• Manual: verified in a live session - links resolve from CalDAV LOCATION, the marker renders on the time line, and clicking opens the browser.

Manual Coverage

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Tested with different bar positions and density settings
• Tested at different interface scaling values
• Tested with multiple monitors

Screenshots / Videos

Checklist

• This PR is ready for review, or it is marked as Draft.
• I read and followed the relevant guidance in CONTRIBUTING.md.
• I ran just format with clang-format v22+ installed, or this PR has no code changes.
• I ran the relevant build or test commands, or explained why they were not run.
• I self-reviewed the changes.
• I checked for new warnings or errors.
• I will update end-user documentation after merge, or this PR does not change user-facing configuration or behavior.
• I added or updated assets/translations/en.json, or this PR adds no new user-facing strings.
• I did not edit non-English translation files unless this PR is explicitly for translation tooling, an import/export sync, or a maintainer-requested locale change.
• I used the existing canonical names for config keys, IPC names, paths, and identifiers.

Additional Notes

• No config option: rows without a link render exactly as before, so there is nothing to opt out of.
• DESCRIPTION is not scanned. It carries dial-in numbers, unsubscribe links and HTML, so picking "the" link from it would surface wrong targets. Can be added if real calendars need it.
• conferenceData.entryPoints[] is not walked; hangoutLink covers Google Meet today.
• Cold-cache edge case: a Google event whose link came only from hangoutLink with an empty LOCATION has nothing to backfill from and becomes clickable after the next sync.