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_render.go

@@ -297,8 +297,10 @@ func renderEndAnnouncement(results []showdownResult, g *HoldemGame) string {
 // renderHelpMessage returns the help text for !holdem help.
 func renderHelpMessage() string {
 	return "🎰 **Texas Hold'em Commands**\n\n" +
+		"**Quick Start:**\n" +
+		"`!holdem play [amount]` — Join, add bot, and deal in one command\n\n" +
 		"**Lobby:**\n" +
-		"`!holdem join` — Sit down at the table\n" +
+		"`!holdem join [amount]` — Sit down (optional buy-in amount)\n" +
 		"`!holdem leave` — Leave the table\n" +
 		"`!holdem start` — Start dealing (≥2 players)\n" +
 		"`!holdem addbot` — Add an AI opponent\n\n" +
@@ -306,7 +308,7 @@ func renderHelpMessage() string {
 		"`!holdem fold` — Fold your hand\n" +
 		"`!holdem check` — Check (no bet to call)\n" +
 		"`!holdem call` — Call the current bet\n" +
-		"`!holdem raise <amount>` — Raise to a total of €amount\n" +
+		"`!holdem raise <amount>` — Raise *to* €amount total (not raise *by*)\n" +
 		"`!holdem allin` — Go all-in\n\n" +
 		"**Other:**\n" +
 		"`!holdem status` — Get current table state (DM)\n" +