fix(recurrence): honor BYDAY for weekly RRULE expansion

Expand weekdays in the DTSTART week and advance by Interval weeks from Monday;
add unit coverage for MO/WE/FR and mid-week starts.

test/unit/logic_recurrence_tests.erl

@@ -7,6 +7,7 @@ logic_recurrence_test_() ->
     {"Validate RRULE test", fun test_validate_rrule/0},
     {"Generate daily occurrences test", fun test_daily_occurrences/0},
     {"Generate weekly occurrences test", fun test_weekly_occurrences/0},
+    {"Generate weekly BYDAY occurrences test", fun test_weekly_byday_occurrences/0},
     {"Generate monthly occurrences test", fun test_monthly_occurrences/0},
     {"Generate with count limit test", fun test_count_limit/0},
     {"Generate with until limit test", fun test_until_limit/0}
@@ -71,6 +72,30 @@ test_weekly_occurrences() ->
   ?assertEqual({{2026, 4, 20}, {10, 0, 0}}, lists:nth(1, Occurrences)),
   ?assertEqual({{2026, 5, 11}, {10, 0, 0}}, lists:nth(4, Occurrences)).
 
+test_weekly_byday_occurrences() ->
+  %% Monday start, MO/WE/FR for two weeks → 6 slots
+  StartTime = {{2026, 4, 20}, {10, 0, 0}},
+  RRule = #{
+    freq => <<"WEEKLY">>,
+    interval => 1,
+    byday => [<<"MO">>, <<"WE">>, <<"FR">>]
+  },
+  RangeEnd = {{2026, 5, 1}, {10, 0, 0}},
+
+  Occurrences = logic_recurrence:generate_occurrences(StartTime, RRule, RangeEnd),
+  ?assertEqual(6, length(Occurrences)),
+  ?assertEqual({{2026, 4, 20}, {10, 0, 0}}, lists:nth(1, Occurrences)),
+  ?assertEqual({{2026, 4, 22}, {10, 0, 0}}, lists:nth(2, Occurrences)),
+  ?assertEqual({{2026, 4, 24}, {10, 0, 0}}, lists:nth(3, Occurrences)),
+  ?assertEqual({{2026, 4, 27}, {10, 0, 0}}, lists:nth(4, Occurrences)),
+  ?assertEqual({{2026, 4, 29}, {10, 0, 0}}, lists:nth(5, Occurrences)),
+  ?assertEqual({{2026, 5, 1}, {10, 0, 0}}, lists:nth(6, Occurrences)),
+
+  %% Mid-week DTSTART must not emit earlier weekdays of the same week
+  WedStart = {{2026, 4, 22}, {10, 0, 0}},
+  MidWeek = logic_recurrence:generate_occurrences(WedStart, RRule, {{2026, 4, 24}, {10, 0, 0}}),
+  ?assertEqual([{{2026, 4, 22}, {10, 0, 0}}, {{2026, 4, 24}, {10, 0, 0}}], MidWeek).
+
 test_monthly_occurrences() ->
   StartTime = {{2026, 4, 20}, {10, 0, 0}},
   RRule = #{