feat(calendar): lazy-load events by date range with cache-first refresh

[tompscanlan]

Summary

Addresses feedback about calendar events being stale/out-of-date.

Why replace LiveQuery?

The old approach used a LiveQuery on comp_calendar_event to reactively display events. But LiveQuery's reactivity added no value here — nothing else writes to that table, only our own code after fetching from the OpenMeet API. The result was:

• No date filtering — full-table scan of all events on every render
• No freshness concept — events fetched once stayed forever, even if changed on OpenMeet
• Redundant re-scans — each insert or replace triggered LiveQuery to re-run a query over data we just fetched

What replaces it

A cache-first architecture that lazy-loads events by visible date range:

• SQLite as durable cache: OPFS-backed SQLite gives instant paint on revisit; if cached data is older than 5 minutes, a fresh API fetch runs and replaces it
• Range-based loading: datesSet callback fetches only the month/day the user is viewing, passes startDate/endDate query params to the API
• Race condition handling: generation counter discards stale API responses on rapid navigation

Files changed

File	Change
+page.svelte	Cache-first loading with loadEventsForRange, loadFromSQLite, writeToSQLite, generation counter, loading overlay
calendar-utils.ts (new)	Pure functions extracted from component for testability
calendar-utils.test.ts (new)	16 unit tests
openmeet.ts	Added optional startDate/endDate params to fetchGroupEvents
calendar.svelte.ts	Removed CalendarEvent interface and calendarEventsQuery (replaced by range-based loading)

Test plan

• Unit tests pass (pnpm test — 16 tests in calendar-utils.test.ts)
• Navigate between months — events load per-range, spinner overlays calendar
• Connect/disconnect OpenMeet — events refresh correctly
• Revisit a previously-viewed month — instant paint from cache, no spinner if < 5 min
• Test in non-UTC timezone — date ranges match calendar boundaries