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/birthday.go

@@ -304,14 +304,11 @@ func (p *BirthdayPlugin) CheckAndPost(roomID id.RoomID) error {
 		}
 
 		// Mark as fired (for XP/DM dedup)
-		_, err = d.Exec(
+		db.Exec("birthday: mark fired",
 			`INSERT INTO birthday_fired (user_id, year) VALUES (?, ?)
 			 ON CONFLICT(user_id, year) DO NOTHING`,
 			m.userID, year,
 		)
-		if err != nil {
-			slog.Error("birthday: mark fired", "user", m.userID, "err", err)
-		}
 	}
 
 	return nil
@@ -337,12 +334,9 @@ func (p *BirthdayPlugin) grantBirthdayXP(userID id.UserID, amount int) {
 		return
 	}
 
-	_, err = d.Exec(
+	db.Exec("birthday: log xp",
 		`INSERT INTO xp_log (user_id, amount, reason) VALUES (?, ?, ?)`,
 		string(userID), amount, "birthday")
-	if err != nil {
-		slog.Error("birthday: log xp", "err", err)
-	}
 }
 
 // parseBirthdayDate parses MM-DD or MM-DD-YYYY format.