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/holdem_eval.go

@@ -142,15 +142,8 @@ func awardPotToLastPlayer(g *HoldemGame) (string, id.UserID) {
 	return ann, winner.UserID
 }
 
-// settleNetDeltas credits each player's remaining stack back to their balance.
-// Buy-in was debited at join time, so we credit the full final stack.
-func settleNetDeltas(g *HoldemGame, euro *EuroPlugin) {
-	for _, p := range g.Players {
-		if p.IsNPC || p.State == PlayerSatOut {
-			continue
-		}
-		if p.Stack > 0 {
-			euro.Credit(p.UserID, float64(p.Stack), "holdem_cashout")
-		}
-	}
-}
+// settleNetDeltas is intentionally a no-op.
+// Economy settlement happens at leave time: buy-in is debited at join,
+// full remaining stack is credited at leave/cashout. Per-hand settlement
+// would double-count because the stack already reflects cumulative results.
+func settleNetDeltas(_ *HoldemGame, _ *EuroPlugin) {}