Add forex plugin, stability fixes, and async HTTP dispatch

- Add forex plugin (Frankfurter v2 API) with rate lookups, analysis,
  DM-based alerts, and daily cron poll. Backfills 1 year of history
  on startup for moving averages and buy signal scoring.

- Fix bot hang caused by SQLite lock contention in reminder polling:
  rows cursor was held open while writing to the same DB. Collect
  results first, close cursor, then process. Same fix in milkcarton.

- Add sync retry loop so the bot reconnects after network drops
  instead of silently exiting. StopSync() for clean Ctrl+C shutdown.

- Add panic recovery to all dispatch, syncer, and cron paths.

- Make all HTTP-calling plugin commands async (goroutines) so a slow
  or dead external API cannot block the message dispatch pipeline.
  Affects: lookup, stocks, forex, anime, movies, concerts, gaming,
  retro, wotd, urls, howami.

- Extract DisplayName to Base, add db.Exec helper, convert silent
  error discards across the codebase.

- Fix UNO mercy-kill bug (eliminated bot continues playing), adventure
  DM nag spam, stats column mismatch, per-call regex/replacer allocs.

- Update README: forex commands, Finance section, 47 plugins.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/plugin/milkcarton.go

@@ -240,36 +240,44 @@ func (p *MilkCartonPlugin) getMissingMembers() []missingMember {
 	}
 	defer rows.Close()
 
-	var result []missingMember
+	type candidate struct {
+		userID, lastDate string
+	}
+	var candidates []candidate
 	for rows.Next() {
-		var userID, lastDate string
-		if err := rows.Scan(&userID, &lastDate); err != nil {
+		var c candidate
+		if err := rows.Scan(&c.userID, &c.lastDate); err != nil {
 			continue
 		}
+		candidates = append(candidates, c)
+	}
+	rows.Close()
 
+	var result []missingMember
+	for _, c := range candidates {
 		// Skip excluded users
-		if p.excludeUsers[userID] {
+		if p.excludeUsers[c.userID] {
 			continue
 		}
 
 		// Skip bots (our own user ID)
-		if id.UserID(userID) == p.Client.UserID {
+		if id.UserID(c.userID) == p.Client.UserID {
 			continue
 		}
 
 		// Skip users with active away/afk status
 		var awayStatus int
-		_ = d.QueryRow(`SELECT 1 FROM presence WHERE user_id = ? AND status IN ('away', 'afk')`, userID).Scan(&awayStatus)
+		_ = d.QueryRow(`SELECT 1 FROM presence WHERE user_id = ? AND status IN ('away', 'afk')`, c.userID).Scan(&awayStatus)
 		if awayStatus == 1 {
 			continue
 		}
 
-		lastTime, err := time.Parse("2006-01-02", lastDate)
+		lastTime, err := time.Parse("2006-01-02", c.lastDate)
 		if err != nil {
 			continue
 		}
 		days := int(now.Sub(lastTime).Hours() / 24)
-		result = append(result, missingMember{userID: userID, daysSince: days})
+		result = append(result, missingMember{userID: c.userID, daysSince: days})
 	}
 	return result
 }