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/stocks.go

@@ -76,7 +76,12 @@ func (p *StocksPlugin) OnReaction(_ ReactionContext) error { return nil }
 
 func (p *StocksPlugin) OnMessage(ctx MessageContext) error {
 	if p.IsCommand(ctx.Body, "stock") {
-		return p.handleStock(ctx)
+		go func() {
+			if err := p.handleStock(ctx); err != nil {
+				slog.Error("stocks: handler error", "err", err)
+			}
+		}()
+		return nil
 	}
 	if p.IsCommand(ctx.Body, "stockwatch") {
 		return p.handleStockwatch(ctx)
@@ -152,14 +157,11 @@ func (p *StocksPlugin) fetchStock(ticker string) (*stockCacheEntry, error) {
 
 	// Update cache
 	data, _ := json.Marshal(entry)
-	_, err = d.Exec(
+	db.Exec("stocks: cache write",
 		`INSERT INTO stocks_cache (ticker, data, cached_at) VALUES (?, ?, ?)
 		 ON CONFLICT(ticker) DO UPDATE SET data = ?, cached_at = ?`,
 		ticker, string(data), time.Now().Unix(), string(data), time.Now().Unix(),
 	)
-	if err != nil {
-		slog.Error("stocks: cache write", "err", err)
-	}
 
 	return entry, nil
 }