Coop lockout fix, holidays full list, !fx convert, lottery cleanup

- Co-op: when a run wipes or completes, clear the 99-sentinel combat
  lock for participants and pin combat_actions_used to maxCombatActions.
  Previously the lock only released on the next midnight reset, so
  members were stuck unable to combat for the rest of the day after
  their run ended.
- Holidays: !holidays now prints the full list. Previously it called
  the same featured-only formatter as TwinBee's morning auto-post,
  so users saw the same truncated message twice with a misleading
  "Use !holidays for the full list" hint that pointed at itself.
- Forex: add currency conversion. Auto-detects when the first arg is
  numeric (`!fx 1500 USD EUR`) and also accepts an explicit `convert`
  subcommand. Tolerant parsing: "to"/"into"/"in"/"=" filters, comma
  and k/m suffix support, and any of `1500 USD EUR`, `1500 USD/EUR`,
  `USD/EUR 1500` orderings. Includes parser + comma-formatter tests.
- Lottery: drop 2-match prize tier. At 1/16 odds × €25 it was +EV per
  ticket on its own and bled the community pot (~€775/wk recently),
  preventing jackpot rollover from accumulating. Removed from scoring,
  payout loops, draw announcement, !lottery odds, and !lottery history.
  Match2Winners DB column kept (history rows preserved); always written
  as 0 going forward.
- Lottery: shift week boundary so Sat/Sun return next Monday. Friday's
  23:59 draw used to leave players locked at their 100-ticket cap until
  next Monday rolled in; now the cap resets immediately after the draw.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/lottery_db.go

@@ -37,14 +37,22 @@ type lotteryHistoryRow struct {
 
 // ── Week Helpers ────────────────────────────────────────────────────────────
 
-// lotteryCurrentWeekStart returns Monday of the current week as "2006-01-02".
+// lotteryCurrentWeekStart returns the Monday of the lottery week currently
+// accepting tickets. Mon–Fri returns this week's Monday; Sat–Sun returns
+// next week's Monday — the Friday 23:59 UTC draw resets the week boundary,
+// so Saturday onward, ticket purchases count toward the next draw.
 func lotteryCurrentWeekStart() string {
 	now := time.Now().UTC()
-	weekday := int(now.Weekday())
-	if weekday == 0 {
-		weekday = 7 // Sunday = 7
+	wd := now.Weekday() // Sunday=0, Monday=1, ..., Saturday=6
+	var monday time.Time
+	switch wd {
+	case time.Sunday:
+		monday = now.AddDate(0, 0, 1)
+	case time.Saturday:
+		monday = now.AddDate(0, 0, 2)
+	default:
+		monday = now.AddDate(0, 0, -(int(wd) - 1))
 	}
-	monday := now.AddDate(0, 0, -(weekday - 1))
 	return monday.Format("2006-01-02")
 }