fix: import weekday-only recurring events (FREQ=DAILY;BYDAY)

[MiMoHo]

Type of change(s)

• Bug fix

What changed and why

Recurring events exported as RRULE:FREQ=DAILY;BYDAY=MO,TU,WE,TH,FR without an INTERVAL field (the format Thunderbird / DAVx5 use for "repeat every weekday") were imported as plain every-day events and therefore also appeared on Saturdays and Sundays (issue #232).

In Parser.parseRepeatInterval(), the FREQ=DAILY branch that converts a weekday-restricted daily rule into a weekly repetition was gated on the RRULE containing INTERVAL:

} else if (value == DAILY && fullString.contains(INTERVAL)) {

When only BYDAY (and no INTERVAL) is present, this branch is skipped, so repeatInterval stays DAY (86400). The later BYDAY handler is then a no-op because repeatInterval.isXWeeklyRepetition() is false for a daily interval, so no weekday bitmask is ever applied and the event repeats every day.

The fix enters the branch when either INTERVAL or BYDAY is present, and additionally guards the "interval is a multiple of 7" check with an INTERVAL presence test (so BYDAY-only rules fall through to the BYDAY conversion and never call interval.toInt() on a non-numeric value):

} else if (value == DAILY && (fullString.contains(INTERVAL) || fullString.contains("BYDAY"))) {
    val interval = fullString.substringAfter("$INTERVAL=").substringBefore(";")
    if (fullString.contains(INTERVAL) && interval.areDigitsOnly() && interval.toInt() % 7 == 0) {
        ...
    } else if (fullString.contains("BYDAY")) {
        repeatInterval = WEEK_SECONDS
    }
}

This sets repeatInterval = WEEK_SECONDS (604800), so the existing BYDAY handler produces the correct Mon-Fri bitmask, making FREQ=DAILY;BYDAY=... behave identically to FREQ=WEEKLY;BYDAY=.... All previously handled cases (plain FREQ=DAILY, FREQ=DAILY;INTERVAL=n, FREQ=DAILY;INTERVAL=14, FREQ=DAILY;INTERVAL=1;BYDAY=...) keep their prior behavior.

Tests performed

Built the fossDebug variant and verified on an Android 15 (API 35) emulator:

Imported ICS with RRULE:FREQ=DAILY;BYDAY=MO,TU,WE,TH,FR (DTSTART Mon 2026-07-06). Month view shows 'Weekday standup' on every weekday (Mon-Fri) and absent on all weekends. Event detail shows repetition = Weekly, Repeat on Mon,Tue,Wed,Thu,Fri (not plain Daily).

Also confirmed detekt, lint, unit tests and the build all pass locally (CI-equivalent).

Closes the following issue(s)

• Closes "repeat every weekday" events from Thunderbird show every day in Fossify #232

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator.
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.

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